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6th Year HL · Mathematics
Derivatives · Derivatives

Differentiation rules and derivatives of standard functions

Aoife is tracking a drone for her Transition Year mini-company video above the Cliffs of Moher. Its height changes with time, and she needs its vertical velocity at any instant. Over an interval, the average rate of change of $f$ on $[a, b]$ is $\dfrac{f(b)-f(a)}{b-a}$, the slope of the chord. As the interval shrinks, it approaches the instantaneous rate of change $f'(a)$, so a small interval gives a good estimate of the slope of the tangent. That means differentiating a function that mixes products, exponentials and chains. The product, quotient and chain rules and the table of standard derivatives are the tools you need. In Leaving Certificate Higher Level, questions combine several rules at once and often end with a trigonometric or logarithmic simplification. Many of these results are in the Formulae and Tables booklet. We come back to Aoife's drone in the last section.

Quick revision: product, quotient and chain rules

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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:

  1. a) $f(x) = (2x + 3)^5$
  1. b) $g(x) = e^{x^2 - 1}$
Solve
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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:

$f(x) = \cos^3(e^{x^2+1})$

Solve
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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:

  1. a) The first derivative $f'(x)$.
  2. b) The second derivative $f''(x)$, simplifying the result using standard trigonometric functions.
Solve

Power rule and powers of $x$

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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):

  1. a) $f(x) = x^7 - 5x^3 + \pi$
  1. b) $g(x) = \sqrt{x} + \frac{1}{x^2}$
Solve
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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.

1. Root to Power ⁿ√x = x¹/ⁿ ³√x = x¹/³ 2. Power Rule f(x) = xⁿ f'(x) = n·xⁿ⁻¹
Solve

Revision: table of standard functions

Graph of the inverse tangent of x over two and of its derivative function, highlighting the gradient at the point x equal to two. (2, π/4) tan⁻¹(x/2) f′(2) = 1/4 f′(x) = 2/(4+x²) 2
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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.

Solve
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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:

  1. a) $f(x) = 4 \times \ln(x) + \log_{2}(x)$
  1. b) $g(x) = 3^x - 5 \times \sin(x)$
Solve
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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 $x = 2$.

Graph of f(x) = arctan(x/2) with its horizontal asymptotes and the point P of the curve with abscissa x = 2 y = π/2 y = −π/2 O x y f(x) = arctan(x/2) P 2
Solve
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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?

Solve

Combining several rules and simplifying

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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.

Solve
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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.

  1. a) Calculate the function that represents the drone's vertical velocity, $v(t) = h'(t)$.
  1. b) What is the drone's vertical velocity at time $t = 5$ seconds?
Graph of the drone's height h(t) in meters versus time in seconds, with the point corresponding to t = 5 s marked 5 10 15 20 t (s) 10 20 30 h(t) (m) t = 5 h(t) = 15t·e⁻⁰·²ᵗ
Solve
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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 $x''(t) + 4x'(t) + 13x(t) = 0$.

t x(t) x(t) = e⁻²ᵗ·cos(3t)
Solve

Logarithmic differentiation among the standard functions

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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 $x > 0$.

Solve
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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 $x = 1$.

Solve

Implicit differentiation, piecewise functions and rates

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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.

Solve
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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:

$$x^2 \times y + y^3 = 10$$
  1. a) Find the expression for the derivative $y'$ in terms of $x$ and $y$ using implicit differentiation.
  2. b) Find the equation of the normal line to the curve at the point $P(3, 1)$.
Solve
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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 $x = 1$.

Solve
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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.

V(t) = 20·e⁰·⁵ᵗ A(t) = π·r(t)² r'(2) = ? h = 0.1 r(t)
Solve

Higher derivatives and partial fractions

To find the nth derivative of a rational function, first split it into partial fractions, then spot the pattern for $\dfrac{1}{x-a}$.

Stationary points and minimum distance

To find where a quantity is smallest or largest, differentiate and solve $f'(x) = 0$. These are the stationary points (turning points).

Summary

See all the exercises in this section