Chapter 0

Math Review for Calculus-Based Physics

This chapter reviews the core algebra and calculus tools that you will use throughout a calculus-based physics course. We begin with the real number system and interval notation, then review functions, domain, and range.

0.1Real Number System and Intervals

In physics, we use the real numbers \(\mathbb{R}\) to describe measurable quantities such as position, time, mass, temperature, and energy. Within \(\mathbb{R}\) there are several important subsets that you should recognize.

0.1.1Standard number sets and notation

We use the following symbols for common number sets:

These sets are nested as

\begin{equation} \mathbb{N}\subset \mathbb{Z}\subset \mathbb{Q}\subset \mathbb{R}, \label{eq:number-sets-chain} \end{equation}

and the set of irrational numbers is

\begin{equation} \mathbb{R}\setminus\mathbb{Q} = \{\text{real numbers that are not rational}\}. \label{eq:irrationals-def} \end{equation}

Sometimes we further distinguish:

Both algebraic and transcendental numbers are real; many of them are irrational.

0.1.2Venn diagram of number sets

Figure 0.1 shows how these sets fit together as nested regions.

Venn diagram illustrating the hierarchy of number sets used in physics. Natural numbers N are contained in the integers Z, which are contained in the rational numbers Q. Together with irrational numbers (both algebraic and transcendental), they form the real numbers R.
Figure 0.1. Venn diagram illustrating the hierarchy of number sets used in physics. Natural numbers \(\mathbb{N}\) are contained in the integers \(\mathbb{Z}\), which are contained in the rational numbers \(\mathbb{Q}\). Together with irrational numbers (both algebraic and transcendental), they form the real numbers \(\mathbb{R}\).

0.1.3Intervals and number lines

When we specify the possible values of a physical quantity, we often use interval notation. Some common examples are

\begin{equation} (-\infty,\infty),\qquad (-3,3),\qquad [0,\infty),\qquad (0,\infty). \label{eq:interval-examples} \end{equation}

Key idea.

We also use half-open intervals such as \((0,3]\) or \([0,3)\), and we combine intervals with the union symbol \(\cup\) when a domain has more than one piece (for example, \((-\infty,-1)\cup(1,\infty)\)).

Figure 0.2 shows two common intervals on a number line.

Examples of open intervals on a number line.
Figure 0.2. Examples of open intervals on a number line.

In later sections, we will use interval notation to describe the domain and range of functions arising in physics.

0.2Functions, Domain, and Range

A function \(f\) from a set \(A\) to a set \(B\) is a rule that assigns to each input \(x\in A\) exactly one output \(f(x)\in B\). We write

\begin{equation} f\colon A\to B,\qquad x\mapsto f(x). \label{eq:function-map} \end{equation}

In physics, the physical domain is often a subset of the mathematical domain. For example:

Throughout this course, always ask:

Which values of the variables make sense in this physical situation?

Those values determine the domain you should use when interpreting graphs, solving equations, or evaluating integrals in physics problems.

0.3Linear Functions and Linear Equations

In this section we first review the algebra of linear functions and linear equations. After each mathematical idea, we point out typical physics situations where exactly the same mathematics appears.

Linear ideas show up everywhere in physics: straight-line graphs, proportional relationships, and first-order (tangent-line) approximations to more complicated functions.

0.3.1Linear functions

A linear function of a real variable \(x\) has the form

\begin{equation} f(x) = m x + b, \label{eq:linear-function} \end{equation}

where

\begin{equation} m = \text{slope}, \qquad b = \text{$y$-intercept}. \label{eq:slope-intercept} \end{equation}

When we draw the graph of \(f\) in the \(xy\)–plane, we usually rename the dependent variable as

\begin{equation} y = f(x) = m x + b. \label{eq:linear-y-form} \end{equation}

The slope \(m\) measures how much \(y\) changes when \(x\) increases by one unit; the intercept \(b\) is the value of \(y\) when \(x=0\).

Physics connection. In physics we often graph one measurable quantity as a function of another. When that graph is a straight line, the relationship between the variables is linear:

In each case one quantity plays the role of \(x\) (independent variable) and the other plays the role of \(y\) (dependent variable), and the graph is a straight line over the range where the linear model is valid.

0.3.2Example: \(f(x)=2x+4\)

Example - Linear function \(f(x)=2x+4\)

Consider

\begin{equation} f(x) = 2x + 4. \label{eq:linear-example} \end{equation}

Comparing with Equation \(\eqref{eq:linear-function}\), we identify

\begin{equation} m = 2, \qquad b = 4. \label{eq:linear-example-mb} \end{equation}

Thus the graph is a straight line of slope \(2\) that crosses the \(y\)-axis at \(y=4\).

Table 0.1 lists some points \((x,f(x))\) on the line, and Figure 0.3 shows the corresponding graph. In the table, the step size in \(x\) is \(1\); in problems you can choose any convenient set of \(x\) values in the domain.

\(x\)\(-3\)\(-2\)\(-1\)\(0\)\(1\)\(2\)\(3\)
\(f(x)\)\(-2\)\( 0\)\( 2\)\(4\)\(6\)\(8\)\(10\)
Table 0.1. Sample values for the linear function \(f(x)=2x+4\).
Graph of the linear function f(x)=2x+4 with several plotted points (x,f(x)).
Figure 0.3. Graph of the linear function \(f(x)=2x+4\) with several plotted points \((x,f(x))\).

Physics connection. You can read this graph the same way you would read, for example, a graph of position \(x(t)\) versus time \(t\) for motion with constant velocity: the slope gives the rate of change, and the intercept gives the initial value.

0.3.3Slope as “rise over run” and as an angle

Now suppose we know two points \((x_1,y_1)\) and \((x_2,y_2)\) on a non-vertical line. The slope \(m\) of that line is

\begin{equation} m = \frac{\Delta y}{\Delta x} = \frac{y_2 - y_1}{x_2 - x_1}, \qquad x_1 \neq x_2. \label{eq:slope-delta} \end{equation}

Here \(\Delta y = y_2 - y_1\) is the rise and \(\Delta x = x_2 - x_1\) is the run.

If the line makes an angle \(\theta\) with the positive \(x\)-axis, then from basic trigonometry the slope is also

\begin{equation} m = \tan\theta. \label{eq:slope-tan} \end{equation}

Thus algebra (slope) and trigonometry (tangent) describe the same geometric idea.

Figure 0.4 shows a slope triangle illustrating \(\Delta x\), \(\Delta y\), and the angle \(\theta\).

Slope triangle for a linear function. The slope is m= y/ x=.
Figure 0.4. Slope triangle for a linear function. The slope is \(m=\Delta y/\Delta x=\tan\theta\).

Physics connection. In physics graphs, the slope often has a direct physical meaning:

Later you will see many examples where reading the slope of a graph is the fastest way to extract a physical quantity.

0.3.4Solving linear equations and manipulating formulas

A linear equation in one unknown \(x\) has the form

\begin{equation} a x + b = 0, \qquad a \neq 0. \label{eq:linear-equation-standard} \end{equation}

To solve for \(x\) we isolate it step by step:

\begin{equation} a x + b = 0 \quad\Rightarrow\quad a x = -b \quad\Rightarrow\quad x = -\frac{b}{a}. \label{eq:linear-solve} \end{equation}

More generally, for

\begin{equation} a x + b = c, \qquad a \neq 0, \label{eq:linear-equation-general} \end{equation}

we obtain

\begin{equation} a x + b = c \quad\Rightarrow\quad a x = c - b \quad\Rightarrow\quad x = \frac{c - b}{a}. \label{eq:linear-solve-general} \end{equation}

Physics connection. In physics we constantly rearrange formulas to solve for a different variable. The algebra is the same as in Equations \(\eqref{eq:linear-equation-standard}\)\(\eqref{eq:linear-solve-general}\).

For example, the constant-acceleration kinematic relation

\begin{equation} x = x_0 + v_0 t + \frac{1}{2} a t^2 \label{eq:kinematic-formula} \end{equation}

can be viewed as:

The structure “coefficient \(\times\) unknown \(+\) constant” is the same as in Equation \(\eqref{eq:linear-equation-general}\); only the names of the symbols change.

0.3.5Solving a system of two linear equations

Sometimes there are two unknown quantities that are tied together by two linear equations. A system of two linear equations in the variables \(x\) and \(y\) has the general form

\begin{align} a_1 x + b_1 y &= c_1, \label{eq:two-eq-general-1} \\ a_2 x + b_2 y &= c_2, \label{eq:two-eq-general-2} \end{align}

where \(a_1, b_1, c_1, a_2, b_2, c_2\) are known numbers. Geometrically, each equation represents a straight line in the \(xy\)-plane, and the solution \((x,y)\) is the point where the two lines intersect.

There are several algebraic methods to solve such systems. Two of the most useful are substitution and elimination.

Method 1: Substitution

  1. Solve one of the equations for one variable in terms of the other.

  2. Substitute that expression into the second equation. This leaves a single equation for one unknown.

  3. Solve for that unknown, then substitute back to find the other variable.

  4. Check the solution in both original equations.

Method 2: Elimination

  1. Multiply one or both equations by suitable constants so that the coefficient of \(x\) or \(y\) is the same (or opposite) in both equations.

  2. Add or subtract the two equations to eliminate one variable.

  3. Solve the resulting single equation for the remaining variable.

  4. Substitute back into either original equation to find the other variable, and check.

Example: Solving a \(2\times 2\) system

Problem. Solve the system

\begin{align} 3x + 2y &= 4, \label{eq:lin-system-ex-1} \\ -6x + y &= 17. \label{eq:lin-system-ex-2} \end{align}

Solution (by substitution).

From Equation \(\eqref{eq:lin-system-ex-2}\) we solve for \(y\):

\begin{equation} -6x + y = 17 \quad\Rightarrow\quad y = 17 + 6x. \label{eq:lin-system-ex-y} \end{equation}

Substitute this into Equation \(\eqref{eq:lin-system-ex-1}\):

\begin{align} 3x + 2y &= 4, \nonumber\\ 3x + 2\bigl(17 + 6x\bigr) &= 4, \nonumber\\ 3x + 34 + 12x &= 4, \nonumber\\ 15x + 34 &= 4. \label{eq:lin-system-ex-sub} \end{align}

Now solve for \(x\):

\begin{equation} 15x = 4 - 34 = -30 \quad\Rightarrow\quad x = \frac{-30}{15} = -2. \label{eq:lin-system-ex-x} \end{equation}

Insert \(x=-2\) into Equation \(\eqref{eq:lin-system-ex-y}\):

\begin{equation} y = 17 + 6(-2) = 17 - 12 = 5. \label{eq:lin-system-ex-y-final} \end{equation}

So the solution is

\begin{equation} (x,y) = (-2,\,5). \end{equation}

Check. Substitute into both original equations:

\begin{align*} 3(-2) + 2(5) &= -6 + 10 = 4, \\ -6(-2) + 5 &= 12 + 5 = 17. \end{align*}

Both equations are satisfied, so \((x,y)=(-2,5)\) is correct.

Physics connection. Systems like \(\eqref{eq:two-eq-general-1}\)\(\eqref{eq:two-eq-general-2}\) appear whenever two unknown quantities are linked by two independent relationships. For example:

The algebra of solving a \(2\times 2\) system is the same in all of these situations; only the physical meaning of \(x\) and \(y\) changes.

Key algebra skills.

0.4Quadratic Functions and Equations

A quadratic function is any function that can be written in the form

\begin{equation} f(x) = a x^2 + b x + c, \qquad a \neq 0, \label{eq:quadratic-general} \end{equation}

where \(a\), \(b\), and \(c\) are real constants. Its graph is a parabola opening upward if \(a>0\) and downward if \(a<0\).

Physics connection. Quadratic functions appear whenever there is constant acceleration or a similar second-order effect:

In both examples, \(x\) or \(y\) is a quadratic function of \(t\).

0.4.1The basic parabola \(f(x)=x^2\)

Example - Basic parabola \(f(x)=x^2\)

The simplest quadratic is

\begin{equation} f(x) = x^2. \label{eq:basic-parabola} \end{equation}

Its graph is a parabola opening upward with vertex at \((0,0)\) and axis of symmetry the \(y\)-axis.

Table 0.2 lists several points \((x,f(x))\) with step size \(1\). In problems you can choose any convenient set of points in the domain.

\(x\)\(-3\)\(-2\)\(-1\)\(0\)\(1\)\(2\)\(3\)
\(f(x)=x^2\)\(9\)\(4\)\(1\)\(0\)\(1\)\(4\)\(9\)
Table 0.2. Sample values of the quadratic function \(f(x)=x^2\). The table makes the symmetry \(f(-x)=f(x)\) visible.
Parabola f(x)=x^2 with selected points (x,f(x)). The graph is symmetric about the y-axis.
Figure 0.5. Parabola \(f(x)=x^2\) with selected points \((x,f(x))\). The graph is symmetric about the \(y\)-axis.

0.4.2Example: \(f(x)=x^2-x-2\)

Example - Quadratic \(f(x)=x^2-x-2\)

Consider

\begin{equation} f(x) = x^2 - x - 2. \label{eq:quadratic-example} \end{equation}

Here \(a=1\), \(b=-1\), and \(c=-2\). Factoring gives

\begin{equation} x^2 - x - 2 = (x-2)(x+1), \label{eq:quadratic-factor} \end{equation}

so the zeros (roots) are

\begin{equation} x = -1 \quad\text{and}\quad x = 2. \label{eq:quadratic-zeros} \end{equation}

Vertex form (useful for sketching). Every quadratic can also be written as

\begin{equation} f(x) = a(x-h)^2 + k, \qquad h = -\frac{b}{2a},\quad k = f(h), \label{eq:vertex-form} \end{equation}

where \((h,k)\) is the vertex. For \(f(x)=x^2-x-2\), we have

\begin{equation} h = -\frac{b}{2a} = \frac{1}{2}, \qquad k = f\!\left(\frac{1}{2}\right) = -\frac{9}{4}, \label{eq:example-vertex} \end{equation}

so the vertex is at \(\bigl(\tfrac{1}{2}, -\tfrac{9}{4}\bigr)\).

Figure 0.6 shows the graph of \(f(x)=x^2-x-2\) with its zeros marked.

Quadratic function f(x)=x^2-x-2 with zeros at x=-1 and x=2. The parabola opens upward since a&gt;0.
Figure 0.6. Quadratic function \(f(x)=x^2-x-2\) with zeros at \(x=-1\) and \(x=2\). The parabola opens upward since \(a>0\).

0.4.3Quadratic equations

A quadratic equation in \(x\) has the standard form

\begin{equation} a x^2 + b x + c = 0, \qquad a \neq 0. \label{eq:quadratic-standard} \end{equation}

Factoring (when possible). If the quadratic factors as

\begin{equation} x^2 + p x + q = (x-r)(x-s), \qquad r+s = -p,\quad rs = q, \label{eq:quad-factor-general} \end{equation}

then the solutions are \(x=r\) and \(x=s\). This is the fastest method when the factors are easy to see.

Quadratic formula (always works). In general, the solutions of \(\eqref{eq:quadratic-standard}\) are given by

\begin{equation} x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}. \label{eq:quadratic-formula} \end{equation}

The quantity

\begin{equation} D = b^2 - 4ac \label{eq:discriminant} \end{equation}

is called the discriminant and determines the type of roots:

In kinematics problems, equations like \(\eqref{eq:projectile-y}\) or \(\eqref{eq:kinematics-x}\) often lead to a quadratic equation for the time \(t\). You should be comfortable choosing between factoring (when possible) and the quadratic formula, and interpreting which root is physically meaningful (for example, discarding negative times when \(t\ge 0\)).

0.5Exponential and Logarithmic Functions

In this book, \(\ln x\) denotes the natural logarithm (logarithm base \(e\)). We sometimes write \(\log x\) when the base is clear from context; unless stated otherwise, it always means \(\ln x\).

The basic exponential and logarithmic functions have

\begin{align} f(x) &= e^x: &&\text{domain }(-\infty,\infty),\quad \text{range }(0,\infty), \label{eq:exp-domain-range} \\ f(x) &= \ln(x): &&\text{domain }(0,\infty),\quad \text{range }(-\infty,\infty). \label{eq:log-domain-range} \end{align}

They are inverse functions:

\begin{equation} e^{\ln x} = x \quad (x>0), \qquad \ln(e^x) = x \quad (x\in\mathbb{R}). \label{eq:exp-log-inverse} \end{equation}

0.5.1Why physics cares

Exponential function y=e^x and natural logarithm y= x, together with the line y=x. The two curves are reflections of each other across y=x, showing that they are inverse functions.
Figure 0.7. Exponential function \(y=e^x\) and natural logarithm \(y=\ln x\), together with the line \(y=x\). The two curves are reflections of each other across \(y=x\), showing that they are inverse functions.

0.5.2Laws of exponents and radicals

For real numbers \(x,y>0\) and integers \(m,n\), the basic exponent rules are

\begin{align} x^m x^n &= x^{m+n}, & \frac{x^m}{x^n} &= x^{m-n} \quad (x\ne 0), \label{eq:exp-laws-1} \\ (x^m)^n &= x^{mn}, & (xy)^n &= x^n y^n, \label{eq:exp-laws-2} \\ x^{-n} &= \frac{1}{x^n}, & x^{1/n} &= \sqrt[n]{x}. \label{eq:exp-laws-3} \end{align}

Fractional exponents correspond to roots and powers:

\begin{equation} x^{m/n} = \bigl(\sqrt[n]{x}\bigr)^m = \sqrt[n]{x^m}, \qquad x>0. \label{eq:fractional-exponent} \end{equation}

These rules are heavily used when simplifying expressions such as \(e^{2kt} = (e^{kt})^2\) or \(\sqrt{ab} = a^{1/2} b^{1/2}\).

0.5.3Logarithm rules

For \(a>0\), \(a\neq 1\), and \(x,y>0\), logarithms satisfy

\begin{align} \ln(xy) &= \ln x + \ln y, \label{eq:log-product} \\ \ln\!\left(\frac{x}{y}\right) &= \ln x - \ln y, \label{eq:log-quotient} \\ \ln(x^k) &= k\,\ln x \quad (k\in\mathbb{R}). \label{eq:log-power} \end{align}

More generally, for a logarithm with base \(a\),

\begin{equation} \log_a x = \frac{\ln x}{\ln a}, \label{eq:change-of-base} \end{equation}

which is the change-of-base formula. In practice we usually work with \(\ln\) and use \(\eqref{eq:change-of-base}\) if another base is needed.

These rules let you turn products into sums and powers into factors, which is especially useful when solving exponential equations and working with logarithmic data in physics.

0.6Trigonometry for Physics

Trigonometry appears everywhere in calculus-based physics: resolving vectors into components, describing oscillations and waves, working with circular motion, and understanding phase in AC circuits. This section reviews the essentials you will use most often.

0.6.1Right-triangle definitions

In a right triangle, let \(\theta\) be one of the acute angles. Then

\begin{equation} \sin\theta=\frac{\text{opposite}}{\text{hypotenuse}},\qquad \cos\theta=\frac{\text{adjacent}}{\text{hypotenuse}},\qquad \tan\theta=\frac{\text{opposite}}{\text{adjacent}}. \label{eq:right-trig-def} \end{equation}

These definitions are ratios of side lengths.

The Pythagorean theorem relates the three sides:

\begin{equation} (\text{hypotenuse})^2 = (\text{adjacent})^2 + (\text{opposite})^2. \label{eq:pythagorean-theorem} \end{equation}

Figure 0.8 shows how the sides are named relative to the angle \(\theta\).

Naming the sides of a right triangle relative to the angle . These labels are used in the definitions of , , and in eq:right-trig-def.
Figure 0.8. Naming the sides of a right triangle relative to the angle \(\theta\). These labels are used in the definitions of \(\sin\theta\), \(\cos\theta\), and \(\tan\theta\) in \(\eqref{eq:right-trig-def}\).

0.6.2Unit circle and special angles

The unit circle (radius \(1\)) encodes all sine and cosine values. For an angle \(\theta\) measured from the positive \(x\)-axis, the point on the circle has coordinates

\begin{equation} (\cos\theta,\sin\theta). \label{eq:unit-circle-coordinates} \end{equation}

Figure 0.9 shows the standard special angles that occur frequently in physics and calculus.

Unit circle with commonly used angles in radians. For each angle the point on the circle has coordinates (,).
Figure 0.9. Unit circle with commonly used angles in radians. For each angle \(\theta\) the point on the circle has coordinates \((\cos\theta,\sin\theta)\).

0.6.3Exact values at common angles

Table 0.3 summarizes the exact values used frequently in physics and calculus.

\(\theta\) (deg)\(0^\circ\)\(30^\circ\)\(45^\circ\)\(60^\circ\)\(90^\circ\)\(180^\circ\)\(270^\circ\)\(360^\circ\)
\(\theta\) (rad)\(0\)\(\pi/6\)\(\pi/4\)\(\pi/3\)\(\pi/2\)\(\pi\)\(3\pi/2\)\(2\pi\)
\(\sin\theta\)\(0\)\(1/2\)\(1/\sqrt{2}\)\(\sqrt{3}/2\)\(1\)\(0\)\(-1\)\(0\)
\(\cos\theta\)\(1\)\(\sqrt{3}/2\)\(1/\sqrt{2}\)\(1/2\)\(0\)\(-1\)\(0\)\(1\)
\(\tan\theta\)\(0\)\(1/\sqrt{3}\)\(1\)\(\sqrt{3}\)undefined\(0\)undefined\(0\)
Table 0.3. Exact values of \(\sin\theta\), \(\cos\theta\), and \(\tan\theta\) at commonly used angles. Angles must be in radians when used in calculus formulas.

0.6.4Graphs of \(\sin x\) and \(\cos x\)

Figure 0.10 shows the graphs of \(f(x)=\sin x\) and \(g(x)=\cos x\) over two periods. Both have domain \((-\infty,\infty)\) and range \([-1,1]\).

Graphs of y= x (solid) and y= x (dashed) over two full periods. Both have amplitude 1 and period 2.
Figure 0.10. Graphs of \(y=\sin x\) (solid) and \(y=\cos x\) (dashed) over two full periods. Both have amplitude \(1\) and period \(2\pi\).

Physics connection. In simple harmonic motion and wave problems, you will repeatedly work with functions of the form

\begin{equation} x(t) = A\cos(\omega t + \phi) \quad\text{or}\quad x(t) = A\sin(\omega t + \phi), \label{eq:shm-trig} \end{equation}

where \(A\) is the amplitude, \(\omega\) is the angular frequency, and \(\phi\) is the phase. Understanding the basic graphs of \(\sin\) and \(\cos\) makes these models much easier to interpret.

0.6.5Key trigonometric identities

Several identities show up repeatedly in physics, especially when simplifying expressions for waves, oscillations, and vector components.

0.6.5.1Pythagorean identities

The Pythagorean identity follows directly from the unit circle:

\begin{equation} \sin^{2}\theta + \cos^{2}\theta = 1. \label{eq:pythagorean-identity} \end{equation}

From this, we obtain

\begin{align} 1 + \tan^{2}\theta &= \sec^{2}\theta, \label{eq:tan-sec-identity} \\ 1 + \cot^{2}\theta &= \csc^{2}\theta. \label{eq:cot-csc-identity} \end{align}

0.6.5.2Even/odd and symmetry identities

Sine is an odd function and cosine is an even function:

\begin{equation} \sin(-\theta) = -\sin\theta,\qquad \cos(-\theta) = \cos\theta. \label{eq:even-odd-identities} \end{equation}

Physically, these symmetries are useful when analyzing motion or fields that are symmetric about the origin or the vertical axis.

0.6.5.3Angle addition and subtraction

The angle addition and subtraction formulas are

\begin{align} \sin(\alpha \pm \beta) &= \sin\alpha\cos\beta \pm \cos\alpha\sin\beta, \label{eq:sin-angle-addition} \\ \cos(\alpha \pm \beta) &= \cos\alpha\cos\beta \mp \sin\alpha\sin\beta. \label{eq:cos-angle-addition} \end{align}

These are especially important when combining waves with different phases, for example in interference and AC circuit analysis.

0.6.5.4Double-angle formulas

Setting \(\beta=\alpha\) in the angle addition formulas gives the double-angle identities:

\begin{align} \sin(2\theta) &= 2\sin\theta\cos\theta, \label{eq:sin-double-angle} \\ \cos(2\theta) &= \cos^{2}\theta - \sin^{2}\theta = 2\cos^{2}\theta - 1 = 1 - 2\sin^{2}\theta. \label{eq:cos-double-angle} \end{align}

These forms are useful when rewriting expressions like \(\sin^{2}\theta\) or \(\cos^{2}\theta\) in terms of a single cosine with double angle, which appears often in power calculations and intensity formulas.

0.6.5.5Phase-shift identities

It is sometimes convenient to convert between sine and cosine using phase shifts:

\begin{align} \sin\!\left(\theta + \frac{\pi}{2}\right) &= \cos\theta, & \cos\!\left(\theta - \frac{\pi}{2}\right) &= \sin\theta, \label{eq:phase-shift-sin-cos} \\ \sin\!\left(\theta - \frac{\pi}{2}\right) &= -\cos\theta, & \cos\!\left(\theta + \frac{\pi}{2}\right) &= -\sin\theta. \label{eq:phase-shift-sin-cos-negative} \end{align}

In oscillation problems, this shows that any sinusoidal function can be written either as a sine or a cosine with an appropriate phase shift.

0.7Calculus Essentials

0.7.1Limits and continuity (informal view)

A limit describes what values \(f(x)\) gets close to when \(x\) gets close to some number \(a\).

Left and right limits.

If both one–sided limits exist and are equal, we say the (two–sided) limit \(\displaystyle \lim_{x\to a} f(x)\) exists and define

\begin{equation} \lim_{x\to a} f(x) = L \quad\text{to mean}\quad \lim_{x\to a^-} f(x) = \lim_{x\to a^+} f(x) = L. \label{eq:limit-definition-informal} \end{equation}
Definition - Continuity at a point

We say that a function \(f\) is continuous at \(x=a\) if all three of the following are true:

  1. \(f(a)\) is defined;

  2. the left-hand and right-hand limits both exist and are equal:

    \begin{equation} \lim_{x\to a^-} f(x) = \lim_{x\to a^+} f(x) = L; \end{equation}
  3. this common limit equals the function value:

    \begin{equation} f(a) = L. \label{eq:continuity-condition} \end{equation}

In words: as you walk along the graph toward \(x=a\) from either side, you end up at the same height, and that height is exactly the value of the function at \(x=a\).

In this course, you mainly need to recognize simple situations where limits describe slopes, rates, or behavior very close to a point (for example, the instantaneous velocity of a moving object).

Example - Continuous at a point

Consider

\begin{equation} f(x) = 3x - 1. \label{eq:limit-example-function} \end{equation}

For \(x\) near \(2\), \(f(x)\) is near \(5\). In fact

\begin{equation} \lim_{x\to 2^-} f(x) = \lim_{x\to 2^+} f(x) = 3\cdot 2 - 1 = 5, \end{equation}

so \( \displaystyle \lim_{x\to 2} f(x) = 5. \) The function value is

\begin{equation} f(2) = 3\cdot 2 - 1 = 5. \end{equation}

Here

\begin{equation} \lim_{x\to 2^-} f(x) = \lim_{x\to 2^+} f(x) = f(2) = 5, \end{equation}

so \(f\) is continuous at \(x=2\). The graph has no jump or hole at that point.

A continuous function: as x 2 from left or right, f(x) 5, and f(2)=5.
Figure 0.11. A continuous function: as \(x\to 2\) from left or right, \(f(x)\to 5\), and \(f(2)=5\).
Example - Limit exists but not continuous (removable hole)

Now consider the piecewise function

\begin{equation} g(x)= \begin{cases} x^2, & x\neq 1,\\[0.25em] 3, & x=1. \end{cases} \label{eq:piecewise-continuity-example} \end{equation}

For \(x\) close to \(1\) (from either side but not equal to \(1\)), \(g(x)\) behaves like \(x^2\), so

\begin{equation} \lim_{x\to 1^-} g(x) = \lim_{x\to 1^+} g(x) = \lim_{x\to 1} x^2 = 1. \label{eq:limit-g-at-1} \end{equation}

Thus \( \displaystyle \lim_{x\to 1} g(x) = 1. \) However,

\begin{equation} g(1) = 3. \label{eq:g-of-1} \end{equation}

So the left and right limits agree, but they do not equal the function value:

\begin{equation} \lim_{x\to 1} g(x) = 1 \neq g(1) = 3. \end{equation}

Therefore \(g\) is not continuous at \(x=1\). The graph has a “hole” at \((1,1)\) and a filled point at \((1,3)\).

A removable discontinuity: left and right limits at x=1 both equal 1, but g(1)=3, so g is not continuous at x=1.
Figure 0.12. A removable discontinuity: left and right limits at \(x=1\) both equal \(1\), but \(g(1)=3\), so \(g\) is not continuous at \(x=1\).

Physics connection.

0.7.2Derivatives as rates of change

In physics, we are often interested in how one quantity changes as another quantity changes. For example, how position changes with time, or how current changes with time. The mathematical tool that describes an instantaneous rate of change is the derivative.

Average vs. instantaneous rate of change. For a function \(f(x)\), the average rate of change of \(f\) between \(x\) and \(x+h\) (with \(h\neq 0\)) is

\begin{equation} \frac{f(x+h) - f(x)}{h}. \label{eq:average-rate-of-change} \end{equation}

Geometrically, this is the slope of the secant line through the points \(\bigl(x,f(x)\bigr)\) and \(\bigl(x+h,f(x+h)\bigr)\).

If we let \(h\) get closer and closer to \(0\), the secant line approaches the tangent line at \(x\), and the average rate of change approaches the instantaneous rate of change.

Definition - Derivative

The derivative of \(f\) at \(x\) is defined by the limit

\begin{equation} f'(x) = \lim_{h\to 0} \frac{f(x+h) - f(x)}{h}, \label{eq:derivative-definition} \end{equation}

when this limit exists. Geometrically, \(f'(x)\) is the slope of the tangent line to the graph of \(f\) at the point \(\bigl(x,f(x)\bigr)\).

The derivative f&#x27;(x) is the limit of the slopes of secant lines as the second point (open circle) moves toward the point of tangency (solid dot). The secant line (dashed) and tangent line (solid) intersect the curve y=f(x) at different points, making the geometry clear.
Figure 0.13. The derivative \(f'(x)\) is the limit of the slopes of secant lines as the second point (open circle) moves toward the point of tangency (solid dot). The secant line (dashed) and tangent line (solid) intersect the curve \(y=f(x)\) at different points, making the geometry clear.

Physical meaning: position, velocity, and acceleration. Let \(x(t)\) denote the position of a particle along a line as a function of time \(t\).

Note that:

Example - Position, velocity, and acceleration

Suppose the position of a particle moving along a line is

\begin{equation} x(t) = 2t^2 + 3t \quad\text{(meters)}, \label{eq:derivative-example-position} \end{equation}

with time \(t\) measured in seconds. Then the velocity and acceleration are

\begin{align} v(t) &= \frac{dx}{dt} = 4t + 3 \quad\text{(m/s)}, \label{eq:derivative-example-velocity} \\ a(t) &= \frac{dv}{dt} = 4 \quad\text{(m/s$^2$)}. \label{eq:derivative-example-acceleration} \end{align}

At \(t = 1\ \text{s}\),

\begin{equation} v(1) = 7\ \text{m/s}, \qquad a(1) = 4\ \text{m/s}^2. \end{equation}

So at \(t=1\ \text{s}\), the particle is moving to the right at \(7\ \text{m/s}\) and speeding up at a constant rate of \(4\ \text{m/s}^2\).

0.7.3Basic derivative rules

Computing derivatives directly from the limit definition \(\eqref{eq:derivative-definition}\) is usually too slow for real problems. In practice, we use a small set of rules. If \(f\) and \(g\) are differentiable and \(c\) is a constant, then:

Basic algebra and power rules

\begin{align} \frac{d}{dx}(c) &= 0, \label{eq:derivative-constant} \\ \frac{d}{dx}\bigl(x^n\bigr) &= n x^{n-1} \quad\text{(power rule)}, \label{eq:power-rule} \\ \frac{d}{dx}\bigl(f+g\bigr) &= f' + g', \label{eq:derivative-sum} \\ \frac{d}{dx}\bigl(cf\bigr) &= c f', \label{eq:derivative-constant-multiple} \end{align}

Product and quotient rules

\begin{align} \frac{d}{dx}\bigl(fg\bigr) &= f'g + fg' \quad\text{(product rule)}, \label{eq:product-rule} \\ \frac{d}{dx}\left(\frac{f}{g}\right) &= \frac{f'g - fg'}{g^2}, \quad g\ne 0 \quad\text{(quotient rule)}. \label{eq:quotient-rule} \end{align}

Chain rule (functions of functions) If \(y=f(u)\) and \(u=g(x)\), then the chain rule says

\begin{equation} \frac{dy}{dx} = \frac{dy}{du}\frac{du}{dx} = f'\bigl(g(x)\bigr)\,g'(x). \label{eq:chain-rule} \end{equation}

This rule is essential whenever the variable \(x\) is “hidden inside” another function (for example, \(\sin(3x)\) or \(e^{x^2}\)).

Standard derivatives (with \(x\) in radians)

\begin{align} \frac{d}{dx}(e^x) &= e^x, & \frac{d}{dx}(\ln x) &= \frac{1}{x} \quad (x>0), \label{eq:derivative-exp-log} \\ \frac{d}{dx}(\sin x) &= \cos x, & \frac{d}{dx}(\cos x) &= -\sin x, \label{eq:derivative-sin-cos} \\ \frac{d}{dx}(\tan x) &= \sec^2 x. \label{eq:derivative-tan} \end{align}
Example - Using product and chain rules

Let

\begin{equation} f(x) = x^2 e^{3x}. \label{eq:derivative-rules-example-f} \end{equation}

Treat \(x^2\) and \(e^{3x}\) as two factors and use the product rule:

\begin{align} f'(x) &= \frac{d}{dx}\bigl(x^2\bigr) \, e^{3x} + x^2 \, \frac{d}{dx}\bigl(e^{3x}\bigr) \nonumber \\ &= 2x\,e^{3x} + x^2 \bigl( 3e^{3x} \bigr) \quad\text{(chain rule on $e^{3x}$)} \nonumber \\ &= e^{3x}\bigl(2x + 3x^2\bigr). \label{eq:derivative-rules-example-result} \end{align}

In physics, combinations like \(x^2 e^{3x}\) can appear in models of exponentially growing or decaying quantities with additional polynomial factors (for example, certain solutions of differential equations).

0.7.4Integrals as accumulated change

Derivatives measure instantaneous rates of change. Integrals do the opposite: they measure how much a quantity has accumulated as another variable changes.

The definite integral of \(f\) from \(a\) to \(b\) is written

\begin{equation} \int_a^b f(x)\,dx. \label{eq:definite-integral} \end{equation}

Informally, this represents the signed area between the graph \(y=f(x)\) and the \(x\)–axis from \(x=a\) to \(x=b\):

From a physics point of view, the key idea is:

quote If \(f(x)\) is a rate of change of some quantity \(Q\), then the integral of \(f\) over an interval gives the net change in \(Q\) over that interval. quote

Mathematically, if \(F\) is any antiderivative of \(f\) (so \(F'(x)=f(x)\)), then the Fundamental Theorem of Calculus says

\begin{equation} \int_a^b f(x)\,dx = F(b) - F(a). \label{eq:FTC} \end{equation}

Example: displacement from velocity. Let \(x(t)\) be the position of a particle and \(v(t)=dx/dt\) its velocity. Then velocity is the rate of change of position, so the net displacement from time \(t=a\) to \(t=b\) is

\begin{equation} x(b) - x(a) = \int_a^b v(t)\,dt. \label{eq:displacement-integral} \end{equation}

If \(v(t)\ge 0\) on \([a,b]\), the particle is always moving in the positive direction and the integral is the (unsigned) area under the \(v(t)\) graph. If \(v(t)\) changes sign, the integral gives the net displacement (forward minus backward motion).

Velocity–time graph. The gray area under v(t) from t=0 to t=4 equals the displacement x(4)-x(0).
Figure 0.14. Velocity–time graph. The gray area under \(v(t)\) from \(t=0\) to \(t=4\) equals the displacement \(x(4)-x(0)\).
Example - Displacement from velocity

A particle moves along a line with velocity

\begin{equation} v(t) = 3t \quad (\text{m/s}), \label{eq:integral-example-velocity} \end{equation}

for \(0 \le t \le 4\ \text{s}\). Its displacement from \(t=0\) to \(t=4\) is

\begin{align} x(4) - x(0) &= \int_0^4 v(t)\,dt = \int_0^4 3t\,dt \nonumber \\ &= 3 \left[ \frac{t^2}{2} \right]_{0}^{4} = 3 \cdot \frac{16}{2} = 24\ \text{m}. \label{eq:integral-example-displacement} \end{align}

If \(x(0)=0\), then \(x(4)=24\ \text{m}\). Notice that the units work out: (m/s)\(\times\) s \(=\) m.

Other physics examples. The same “rate \(\to\) accumulated change” idea appears everywhere:

0.7.5Indefinite integrals and antiderivative rules

While a definite integral gives a number, an indefinite integral (or antiderivative) gives a family of functions.

Definition - Indefinite integral / antiderivative

A function \(F\) is called an antiderivative of \(f\) on an interval if

\begin{equation} F'(x) = f(x) \quad\text{for all }x\text{ in the interval}. \end{equation}

We write

\begin{equation} \int f(x)\,dx = F(x) + C, \label{eq:indefinite-integral} \end{equation}

where \(C\) is an arbitrary constant. Different choices of \(C\) give different antiderivatives with the same derivative \(f\).

For \(n\ne -1\),

\begin{equation} \int x^n\,dx = \frac{x^{n+1}}{n+1} + C. \label{eq:antiderivative-power} \end{equation}

Other standard examples (again with \(x\) in radians) are

\begin{align} \int e^x\,dx &= e^x + C, & \int \frac{1}{x}\,dx &= \ln|x| + C, \label{eq:antiderivative-exp-log} \\ \int \cos x\,dx &= \sin x + C, & \int \sin x\,dx &= -\cos x + C. \label{eq:antiderivative-sin-cos} \end{align}

In physics, indefinite integrals often appear when we solve differential equations. For example, if we know that acceleration \(a\) is constant, then

\begin{equation} \frac{dv}{dt} = a \quad\Rightarrow\quad v(t) = \int a\,dt = at + C, \end{equation}

and the constant \(C\) is fixed by an initial condition like \(v(0)=v_0\).

\(u\)–substitution (reverse chain rule). When a function has the form \(f(g(x))g'(x)\), a simple substitution \(u=g(x)\) often reduces the integral to one of these basic forms. This is the integration version of the chain rule.

Example - Basic antiderivatives

Compute

\begin{equation} \int \left(3x^2 - \frac{4}{x} + 5\right) dx. \label{eq:antiderivative-rules-example} \end{equation}

Rewrite \(\dfrac{4}{x}\) as \(4x^{-1}\) and integrate term by term:

\begin{align} \int \left(3x^2 - 4x^{-1} + 5\right) dx &= 3 \int x^2 dx - 4 \int x^{-1} dx + 5 \int dx \nonumber \\ &= 3 \cdot \frac{x^{3}}{3} - 4 \ln|x| + 5x + C \nonumber \\ &= x^{3} - 4\ln|x| + 5x + C. \label{eq:antiderivative-rules-example-result} \end{align}
Example - Simple \(u\)–substitution

Compute

\begin{equation} \int 2x \cos(x^2)\,dx. \label{eq:usub-example} \end{equation}

Let \(u=x^2\), so \(du = 2x\,dx\). Then

\begin{align} \int 2x \cos(x^2)\,dx &= \int \cos(u)\,du \nonumber \\ &= \sin(u) + C \nonumber \\ &= \sin(x^2) + C. \label{eq:usub-example-result} \end{align}

This pattern (something like \(\cos(\text{something})\) times the derivative of that “something”) occurs frequently in physics, for example when integrating fields or potentials that have composite functional forms.

For the Interested Reader

This chapter is a fast refresher, not a first course. If a topic here is genuinely new to you rather than just rusty, the resources below teach it properly, and they are the right place to build the fluency this course assumes. Everything listed is free.

Videos

3Blue1Brown's Essence of Calculus is the best visual introduction to the calculus half of this review. It builds the derivative and the integral from pictures, so the rules in the last section stop looking like something to memorise. Start with the overview, then watch the episode matching whatever you want to see:

Video

The essence of calculus — 3Blue1Brown

Video thumbnail for The essence of calculus — 3Blue1BrownWatch on YouTube

Open video on YouTube

For the algebra, trigonometry and precalculus material, Khan Academy's Precalculus track has short videos with immediate practice on exactly the functions, exponentials, logarithms and trigonometry reviewed above.

Websites

Remark

A word on how to use this chapter. Do not try to memorise it. Skim it once to see what is here, then come back to a specific section the moment a physics problem needs it — when you first have to differentiate a trajectory, integrate a velocity, or solve a quadratic for a time of flight. The mathematics sticks far better when a physical question makes you reach for it.