Derivatives of Common Functions
A cell phone cools down on the table, a social network gains users, a spring oscillates: all of these phenomena are modeled with exponentials, logarithms, and sines. To know how fast they change, you need to differentiate each type of basic function. With a fixed table of derivatives and the chain rule, you will be able to differentiate almost any function you encounter in high school.
Exponential and logarithmic functions
Find the derivative of the following composite exponential function: $q(x) = e^{4x^3 - 7x}$
Find the derivative of the following composite exponential function:
$q(x) = e^{4x^3 - 7x}$
Determine the derivative of the following composite logarithmic function: $s(x) = \ln(2x^4 + x^2 - 3)$
Determine the derivative of the following composite logarithmic function:
$s(x) = \ln(2x^4 + x^2 - 3)$
The number of active users of an emerging social network, in thousands, as a function of time $t$ (in months) is given by the expression $U(t) = 50 e^{0.2t^2 - 0.1t}$.…
The number of active users of an emerging social network, in thousands, as a function of time $t$ (in months) is given by the expression $U(t) = 50 e^{0.2t^2 - 0.1t}$. Calculate the instantaneous rate of growth of the number of users at time $t = 3$ months.
Trigonometric functions
Calculate the derivative of the following trigonometric function: $f(x) = 5\sin x - 3\cos x + \tan x$
Calculate the derivative of the following trigonometric function:
$f(x) = 5\sin x - 3\cos x + \tan x$
Repeatedly apply the chain rule to find the derivative of the following trigonometric function: $f(x) = \sin^3(2x^2 + \pi)$
Repeatedly apply the chain rule to find the derivative of the following trigonometric function:
$f(x) = \sin^3(2x^2 + \pi)$
Show, using the quotient rule for differentiation and the fundamental trigonometric identity ($\sin^2 x + \cos^2 x = 1$), that the derivative of the secant function…
Show, using the quotient rule for differentiation and the fundamental trigonometric identity ($\sin^2 x + \cos^2 x = 1$), that the derivative of the secant function $f(x) = \frac{1}{\cos x}$ is $f'(x) = \tan x \times \sec x$.
Powers and roots of a function
Find the derivative of the following polynomial function: $f(x) = 4x^5 - \frac{3}{2}x^4 + 7x^2 - \sqrt{2}x + 5$
Find the derivative of the following polynomial function:
$f(x) = 4x^5 - \frac{3}{2}x^4 + 7x^2 - \sqrt{2}x + 5$
Apply the chain rule to differentiate the following power of a function: $p(x) = (3x^2 - 5x + 1)^4$
Apply the chain rule to differentiate the following power of a function:
$p(x) = (3x^2 - 5x + 1)^4$
Calculate the derivative of the function involving a radical: $r(x) = \sqrt{5x^2 - 3x + 2}$
Calculate the derivative of the function involving a radical:
$r(x) = \sqrt{5x^2 - 3x + 2}$
Inverse trigonometric functions
Calculate the derivative of the following function that combines inverse trigonometric functions with exponentials and polynomials: $h(x) = \arctan(e^x) + \arcsin(2x)$
Calculate the derivative of the following function that combines inverse trigonometric functions with exponentials and polynomials:
$h(x) = \arctan(e^x) + \arcsin(2x)$
Product and quotient with common functions
The functions in the table almost never appear alone: they are combined with products and quotients. The strategy is the same: identify the outer operation, apply its rule, and use the table on each factor. Sometimes it helps to simplify first using properties of logarithms.
Apply the product rule to find the derivative of the function: $g(x) = x^3 \ln x$
Apply the product rule to find the derivative of the function:
$g(x) = x^3 \ln x$
Find the derivative of the following quotient of functions: $h(x) = \frac{e^x}{x^2+1}$
Find the derivative of the following quotient of functions:
$h(x) = \frac{e^x}{x^2+1}$
Use the laws of logarithms to simplify the expression before differentiating, and find the derivative of the function: $g(x) = \ln\left(\sqrt{\frac{x-2}{x+2}}\right)$
Use the laws of logarithms to simplify the expression before differentiating, and find the derivative of the function:
$g(x) = \ln\left(\sqrt{\frac{x-2}{x+2}}\right)$
Applications: rate of change and tangent line
With the table you can now answer questions about change. If $f(t)$ models a quantity, $f'(t)$ is its instantaneous rate of change; and $f'(a)$ is the slope of the tangent line at $x=a$, whose equation is $y-f(a)=f'(a)(x-a)$.
The temperature $T$ (in degrees Celsius) of an industrial engine as a function of time $t$ (in minutes) after being switched off follows Newton's law of cooling, given…
The temperature $T$ (in degrees Celsius) of an industrial engine as a function of time $t$ (in minutes) after being switched off follows Newton's law of cooling, given by $T(t) = 25 + 85 e^{-0.05t}$. Calculate and interpret the value of $T'(10)$, that is, the rate at which the temperature decreases after 10 minutes.
Find the equation of the tangent line to the curve defined by $f(x) = x e^{-2x} + \cos(\pi x)$ at the point with x-coordinate $x = 0$.
Find the equation of the tangent line to the curve defined by $f(x) = x e^{-2x} + \cos(\pi x)$ at the point with x-coordinate $x = 0$.
The total production cost, in pesos, of $q$ units of a high-precision electronic component is modeled by the function $C(q) = \frac{4\,000q^2 + 10\,000}{q+2}$. Calculate…
The total production cost, in pesos, of $q$ units of a high-precision electronic component is modeled by the function $C(q) = \frac{4\,000q^2 + 10\,000}{q+2}$. Calculate the marginal cost $C'(q)$ when exactly $q = 10$ units are produced.
Successive derivatives and the nth derivative
If you differentiate $f'$ you get the second derivative $f''$; if you differentiate again, $f'''$, and so on. This is useful for concavity and inflection points (where $f''=0$), and also for finding a pattern and writing the nth derivative, which is denoted $f^{(n)}(x)$.
The strategy: differentiate three or four times, write each result as a power (with a negative exponent if there is a quotient), and observe what changes: the sign, the coefficient, and the exponent.
Find the general expression for the nth derivative (of order $n$) of the function $f(x) = \ln(2x - 1)$.
Find the general expression for the nth derivative (of order $n$) of the function $f(x) = \ln(2x - 1)$.
In an epidemiological model, the proportion of the population infected by a virus over time $t$ (in weeks) follows a logistic curve given by…
In an epidemiological model, the proportion of the population infected by a virus over time $t$ (in weeks) follows a logistic curve given by $I(t) = \frac{1}{1 + 49e^{-0.5t}}$. Calculate the rate of change of the infection $I'(t)$ and determine in which week the disease spreads most rapidly (that is, the point of inflection where $I''(t) = 0$).
Back to the beginning: cooling, user growth, and the damped spring are all differentiated with the same pieces: exponential, sine or cosine, and the chain rule.