Differentiation Rules and Derivatives of Common Functions
A drone takes off and its height is $h(t) = 15t\,e^{-0.2t}$. How fast is it rising at 5 seconds? Computing the limit with the four-step rule would take forever. That is why differentiation rules exist: shortcuts that come from the definition and that, combined, differentiate almost any function you will run into. At the end of the page we come back to this drone.
Table of common derivatives
Before differentiating a root or a fraction, rewrite it as a power: $\sqrt[3]{x}=x^{1/3}$ and $\dfrac{1}{x^2}=x^{-2}$.
Calculate the derivative function of the following functions by applying the differentiation rules for elementary functions (powers and roots): a)…
Calculate the derivative function of the following functions by applying the differentiation rules for elementary functions (powers and roots):
- a) $f(x) = x^7 - 5x^3 + \pi$
- b) $g(x) = \sqrt{x} + \frac{1}{x^2}$
Find the derivative function of the following transcendental functions using standard derivative tables: a) $f(x) = 4 \times \ln(x) + \log_{2}(x)$ b)…
Find the derivative function of the following transcendental functions using standard derivative tables:
- a) $f(x) = 4 \times \ln(x) + \log_{2}(x)$
- b) $g(x) = 3^x - 5 \times \sin(x)$
Given the function $f(x) = \frac{x^4}{4} - \sqrt[3]{x}$, calculate its derivative function $f'(x)$ and simplify the result, writing the root back in radical form.
Given the function $f(x) = \frac{x^4}{4} - \sqrt[3]{x}$, calculate its derivative function $f'(x)$ and simplify the result, writing the root back in radical form.
Slope and rate of change with the derivative function
The derivative function $f'(x)$ gives the slope of the tangent line at each point and the instantaneous rate of change of $f$. If $f$ is a position, $f'$ is the velocity.
With exponential functions the same thing happens: if $S(t)=150e^{0.4t}$ is the number of followers of an account, $S'(t)=150\cdot 0.4\,e^{0.4t}=60e^{0.4t}$ is new followers per month. (Here we already used that the factor $0.4$ from the chain rule comes out multiplying; the rule is explained in the next section.)
A fireworks rocket takes off vertically from a launch pad. The height $h$ in meters with respect to time $t$ in seconds is given by the polynomial function…
A fireworks rocket takes off vertically from a launch pad. The height $h$ in meters with respect to time $t$ in seconds is given by the polynomial function $h(t) = t^3 - 4t^2 + 5t + 2$. Calculate the derivative function $h'(t)$, which represents the instantaneous velocity of the rocket at any instant $t$.
Given the quadratic function $f(x) = x^2 - 6x + 5$, find: a) The derivative function $f'(x)$. b) The value of the slope of the tangent line to the graph of the function…
Given the quadratic function $f(x) = x^2 - 6x + 5$, find:
- a) The derivative function $f'(x)$.
- b) The value of the slope of the tangent line to the graph of the function at the point $P$ with abscissa $x = 4$ (marked in the figure).
A spring oscillates following simple harmonic motion described by the function $y(x) = 5 \times \cos(x) + 2$, where $y$ is the position in centimeters and $x$ is time.…
A spring oscillates following simple harmonic motion described by the function $y(x) = 5 \times \cos(x) + 2$, where $y$ is the position in centimeters and $x$ is time. Obtain the expression for the derivative function $y'(x)$, which represents the oscillation velocity of the spring.
A social media account has analysed its growth and determined that the number of followers $S$ evolves according to the exponential function…
A social media account has analysed its growth and determined that the number of followers $S$ evolves according to the exponential function $S(t) = 150 \times e^{0.4t}$, where $t$ is the elapsed time in months since its creation. Determine the derivative function $S'(t)$ to find the rate of follower growth.
The chain rule
Strategy: identify the outermost function, differentiate it leaving the inside unchanged, and multiply by the derivative of the inside. If there are several layers, repeat.
Calculate the derivative of the following simple composite functions by applying the chain rule directly: a) $f(x) = (2x + 3)^5$ b) $g(x) = e^{x^2 - 1}$
Calculate the derivative of the following simple composite functions by applying the chain rule directly:
- a) $f(x) = (2x + 3)^5$
- b) $g(x) = e^{x^2 - 1}$
Calculate the derivative function of the following composite function, applying the chain rule and simplifying the result as much as possible: $f(x) = \cos^3(e^{x^2+1})$
Calculate the derivative function of the following composite function, applying the chain rule and simplifying the result as much as possible:
$f(x) = \cos^3(e^{x^2+1})$
Calculate the equation of the tangent line to the curve $f(x) = \arctan\left(\frac{x}{2}\right)$ at the point with abscissa $x = 2$. The figure shows the graph of $f$,…
Calculate the equation of the tangent line to the curve $f(x) = \arctan\left(\frac{x}{2}\right)$ at the point with abscissa $x = 2$.
The figure shows the graph of $f$, its horizontal asymptotes and the point $P$ of the curve whose abscissa is $x = 2$.
Product and quotient
A surveillance drone follows a trajectory whose height in meters is given by the function $h(t) = 15t \times e^{-0.2t}$, where $t$ is the time in seconds since takeoff.…
A surveillance drone follows a trajectory whose height in meters is given by the function $h(t) = 15t \times e^{-0.2t}$, where $t$ is the time in seconds since takeoff.
- a) Calculate the function representing the vertical velocity of the drone, $v(t) = h'(t)$.
- b) What is the vertical velocity of the drone at the instant $t = 5$ seconds?
Given the rational function involving natural logarithms: $g(x) = \frac{\ln(x^2 + 4)}{x}$ Find the expression of its derivative $g'(x)$ and determine the values of $x$…
Given the rational function involving natural logarithms:
$g(x) = \frac{\ln(x^2 + 4)}{x}$
Find the expression of its derivative $g'(x)$ and determine the values of $x$ for which the gradient of the tangent line to the graph of $g(x)$ is equal to zero.
Find the values of the parameters $a, b \in \mathbb{R}$ so that the function $f(x) = a \times \sin(x) + b \times e^{-x}$ satisfies the following conditions…
Find the values of the parameters $a, b \in \mathbb{R}$ so that the function $f(x) = a \times \sin(x) + b \times e^{-x}$ satisfies the following conditions simultaneously:
-
It passes through the point $(0, 3)$.
-
Its derivative at the origin is $f'(0) = 2$.
Simplify before differentiating
Given the function $f(x) = \ln(\cos(x))$, find: a) The first derivative $f'(x)$. b) The second derivative $f''(x)$, simplifying the result using standard trigonometric…
Given the function $f(x) = \ln(\cos(x))$, find:
- a) The first derivative $f'(x)$.
- b) The second derivative $f''(x)$, simplifying the result using standard trigonometric functions.
Calculate the derivative of the function $f(x) = \arctan\left(\frac{x-1}{x+1}\right)$ and simplify the resulting expression. Which simpler function does this derivative…
Calculate the derivative of the function $f(x) = \arctan\left(\frac{x-1}{x+1}\right)$ and simplify the resulting expression. Which simpler function does this derivative correspond to?
Calculate the derivative of the following function, simplifying the final result as much as possible using trigonometric identities:…
Calculate the derivative of the following function, simplifying the final result as much as possible using trigonometric identities:
$f(x) = \ln\left( \sqrt{\frac{1 + \sin x}{1 - \sin x}} \right)$
Calculate the derivative of the following composite function and simplify the result as much as possible using trigonometric identities: $$g(x) = \ln \left(…
Calculate the derivative of the following composite function and simplify the result as much as possible using trigonometric identities:
$$g(x) = \ln \left( \sqrt{\frac{1 + \sin x}{1 - \sin x}} \right)$$What curiosity do you observe in the final simplified result?
Extension techniques: logarithmic differentiation, implicit differentiation, inverse functions, and more
Logarithmic differentiation
If the base and the exponent depend on $x$, as in $u(x)^{v(x)}$, no row of the table works. You take $\ln$ of both sides, differentiate, and solve:
$$\ln f=v\ln u \;\Rightarrow\; \frac{f'}{f}=v'\ln u+v\frac{u'}{u} \;\Rightarrow\; f'=f\left(v'\ln u+v\frac{u'}{u}\right)$$It also works for products and quotients with many factors. The reason: $\ln(u^v)=v\ln u$ brings the exponent down and turns the power into a product, which you do know how to differentiate.
Using logarithmic differentiation, find the derivative of the function $f(x) = x^{\sqrt{x}}$ for $x > 0$.
Using logarithmic differentiation, find the derivative of the function $f(x) = x^{\sqrt{x}}$ for $x > 0$.
Use logarithmic differentiation to find the derivative of the following power-exponential function: $f(x) = (x^2 + 1)^{\sin(x)}$
Use logarithmic differentiation to find the derivative of the following power-exponential function:
$f(x) = (x^2 + 1)^{\sin(x)}$
Given the transcendental function defined by $f(x) = (\arctan x)^x$ for $x > 0$, use the technique of logarithmic differentiation to calculate its derivative function…
Given the transcendental function defined by $f(x) = (\arctan x)^x$ for $x > 0$, use the technique of logarithmic differentiation to calculate its derivative function $f'(x)$. Once obtained, calculate the exact value of the gradient of the tangent line to the graph of $f$ at the point with x-coordinate $x = 1$.
To properly size a steel beam subjected to asymmetric torsion, an engineer needs to optimise a stress function given by…
To properly size a steel beam subjected to asymmetric torsion, an engineer needs to optimise a stress function given by $E(x) = \frac{\sqrt{x^2 - 1} \times e^{3x}}{(2x + 1)^4}$ for $x > 1$. Apply logarithmic differentiation to obtain the simplified expression of the derivative $E'(x)$.
Implicit differentiation
If $y$ is tied to $x$ by an equation such as $x^2y+y^3=10$, you differentiate everything with respect to $x$ treating $y$ as a function of $x$ (with the chain rule: $(y^3)'=3y^2y'$) and solve for $y'$.
Inverse function
If $f$ is differentiable and invertible with $f(a)=b$ and $f'(a)\neq0$, then $(f^{-1})'(b)=\dfrac{1}{f'(a)}$. For example, if $f(x)=x^3+2x+\cos(x-1)$, then $f'(x)=3x^2+2-\sin(x-1)>0$ (because $3x^2+2\ge2>1\ge\sin(x-1)$), so $f$ is strictly increasing and one-to-one and onto on $\mathbb{R}$. Since $f(1)=4$ and $f'(1)=5$, we get $(f^{-1})'(4)=\dfrac15$.
Successive derivatives
You differentiate repeatedly. For $x(t)=e^{-2t}\cos(3t)$, the velocity is $v=x'$ and the acceleration is $a=x''$; both use the product and chain rules.
For a rational function, break it into partial fractions and use the pattern for $\frac{1}{x-a}$:
$$\left(\frac{1}{x-a}\right)'=-\frac{1}{(x-a)^2},\quad \left(\frac{1}{x-a}\right)''=\frac{2}{(x-a)^3},\quad \left(\frac{1}{x-a}\right)^{(n)}=\frac{(-1)^n\,n!}{(x-a)^{n+1}}$$Piecewise functions
To be differentiable at a joining point, the function must be continuous there and the one-sided derivatives must agree. Differentiable implies continuous, but not the other way around.
Related rates and minimum distance
When two quantities are linked and both change with time, you differentiate the relationship with respect to $t$ using the chain rule.
To minimize a distance it is enough to minimize its square: you differentiate and set it equal to zero.
Determine the values of the real parameters $a$ and $b$ so that the following piecewise function is differentiable on its entire domain: $$f(x) = \begin{cases} a \times…
Determine the values of the real parameters $a$ and $b$ so that the following piecewise function is differentiable on its entire domain:
$$f(x) = \begin{cases} a \times e^{x^2-1} + b & \text{if } x \leq 1 \\ \ln(x) + x^2 & \text{if } x > 1 \end{cases}$$Explain, with reasoning, the relationship between continuity and differentiability at the breakpoint $x = 1$.
Consider the curve implicitly defined by the equation: $$x^2 \times y + y^3 = 10$$ a) Find the expression for the derivative $y'$ in terms of $x$ and $y$ using implicit…
Consider the curve implicitly defined by the equation:
$$x^2 \times y + y^3 = 10$$- a) Find the expression for the derivative $y'$ in terms of $x$ and $y$ using implicit differentiation.
- b) Find the equation of the normal line to the curve at the point $P(3, 1)$.
Sea la función $f(x) = x^3 + 2x + \cos(x - 1)$. a) Demuestra que $f(x)$ es biyectiva en todo $\mathbb{R}$ (puedes apoyarte en el estudio de su crecimiento). b) Sabiendo…
Sea la función $f(x) = x^3 + 2x + \cos(x - 1)$.
- a) Demuestra que $f(x)$ es biyectiva en todo $\mathbb{R}$ (puedes apoyarte en el estudio de su crecimiento).
- b) Sabiendo que $f(1) = 4$, calcula el valor de la derivada de la función inversa en ese punto, es decir, $(f^{-1})'(4)$.
Find the general expression of the nth derivative ($f^{(n)}(x)$) for the rational function: $$f(x) = \frac{1}{x^2 - 3x + 2}$$ Hint: Decompose the function into partial…
Find the general expression of the nth derivative ($f^{(n)}(x)$) for the rational function:
$$f(x) = \frac{1}{x^2 - 3x + 2}$$Hint: Decompose the function into partial fractions before beginning successive differentiation.
A surveillance drone moves following the trajectory given by the function $f(x) = \sqrt{x^2 + 1}$. An operator located at point $A(2, 0)$ watches the drone. Calculate…
A surveillance drone moves following the trajectory given by the function $f(x) = \sqrt{x^2 + 1}$. An operator located at point $A(2, 0)$ watches the drone.
Calculate the point on the trajectory where the drone is at the minimum distance from the operator.
Note: To minimize the distance $d$, it is sufficient to minimize the square of the distance $d^2$. You will need to differentiate the resulting distance function.
In a biotechnology laboratory, the volume of a bacterial population (in $mm^3$) grows according to the function $V(t) = 20 \times e^{0.5t}$, where $t$ is time in hours.…
In a biotechnology laboratory, the volume of a bacterial population (in $mm^3$) grows according to the function $V(t) = 20 \times e^{0.5t}$, where $t$ is time in hours. At the same time, the radius of the circular culture dish where the bacteria grow expands such that the area occupied by the population is $A(t) = \pi \times [r(t)]^2$.
Assuming that the thickness of the bacterial layer is constant and equal to $0.1 mm$ (so that $V = A \times h$), calculate the instantaneous rate of change of the radius of the population at time $t = 2$ hours.
A harmonic oscillator in a mechanical system has a position given by $x(t) = e^{-2t} \cos(3t)$. Calculate the velocity $v(t) = x'(t)$ and acceleration $a(t) = x''(t)$,…
A harmonic oscillator in a mechanical system has a position given by $x(t) = e^{-2t} \cos(3t)$. Calculate the velocity $v(t) = x'(t)$ and acceleration $a(t) = x''(t)$, and check whether it satisfies the differential equation $x''(t) + 4x'(t) + 13x(t) = 0$.