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2.06 Differentiation and trigonometric functions

Worksheet
Derivatives of sin(x) and cos(x)
1

Consider the graph of y = \sin x:

-\frac{3}{2}π
-1π
-\frac{1}{2}π
\frac{1}{2}π
\frac{3}{2}π
x
-1
1
y
a

Describe the motion of the graph of y = \sin x.

b

State whether each of the following describes the nature of the gradient of the curve:

i

Between points where the gradient is 0, the gradient is always negative.

ii

The gradient of the curve is 0 once every 2 \pi radians.

iii

Between points where the gradient is 0, the gradient is always positive.

iv

The gradient of the curve is 0 once every \pi radians.

v

Between points where the gradient is 0, the gradient is positive and negative alternately.

c

List the intervals in the above graph in which the gradient of y = \sin x is positive.

d

List the intervals in the above graph in which the gradient of y = \sin x is negative.

e

Given that the gradient at x=0 is 1, sketch a graph of the gradient function y' for -2\pi \leq x \leq 2 \pi.

f

What is the equation of the gradient function y' graphed in the previous part?

2

Consider the graph of y = \cos x:

-\frac{3}{2}π
-1π
-\frac{1}{2}π
\frac{1}{2}π
\frac{3}{2}π
x
-1
1
y
a

Describe the motion of the graph of y = \cos x.

b

State whether each of the following describes the nature of the gradient of the curve:

i

The gradient of the curve is only 0 once every 2 \pi radians.

ii

Between points where the gradient is 0, the gradient is positive and negative alternately.

iii

Between points where the gradient is 0, the gradient is always positive.

iv

Between points where the gradient is 0, the gradient is always negative.

v

The gradient of the curve is 0 once every \pi radians.

c

List the intervals in the above graph in which the gradient of y = \cos x is positive.

d

List the intervals in the above graph in which the gradient of y = \cos x is negative.

e

Given that the gradient at x=\dfrac{\pi}{2} is - 1, sketch a graph of the gradient function y' for -2\pi \leq x \leq 2 \pi.

f

What is the equation of the gradient function y' graphed in the previous part?

3

Consider the function y = \sin a x, where a is a constant.

a

Let u = a x. Rewrite the function in terms of u.

b

Determine \dfrac{d u}{d x}.

c

Hence, determine \dfrac{d y}{d x} in terms of x.

d

Consider the function f \left( x \right) = \sin 3 x. State f' \left( x \right).

e

Hence, evaluate f' \left( \dfrac{\pi}{6} \right).

4

Differentiate the following functions:

a
y=\sin 7 x
b
y=\cos 3 x
c
y = 8 \sin \left(\dfrac{x}{4}\right)
d
y = \sin x + 3 \cos x
e
y = - 3 \sin x
f
y = 2 - 3 \cos x
g
y = 3 x + \sin 5 x
h
y = 3 \cos 4 x + 6 \sin 5 x
i
y = \sin \left(\dfrac{x}{3}\right) - 2 \cos x
j
y = 5 \sin \left(\dfrac{x}{2}\right) + 3x^{2}-x
5

Differentiate the following functions:

a
y = \cos \left(x + \dfrac{\pi}{7}\right)
b
y = \cos \left( 3 x^{2}\right)
c
y = \sin \left(x^{5}\right)
d
y = \sin \left(x^{6} + 5\right)
e
y = \sin \left( 4 x^{5} + 3\right)
f
y = \sin \left(x^{4} + 3\right)
g
y = \cos \left(\dfrac{x^2}{4}\right)
h
y = \cos \left(\dfrac{\pi t}{2} - \dfrac{\pi}{3}\right)
6

Consider the function y = \cos \left( 2 x\right) + x.

a

Differentiate y = \cos \left( 2 x\right) + x.

b

Solve for the first positive value of x at which \dfrac{d y}{d x} = \sqrt{3} + 1. Give your answer in radians.

7

Consider the graph of y = \cos x which is the gradient function of y = \sin x. A number of points have been labelled on the graph:

Name the point on the gradient function that corresponds to the following locations on the graph of y = \sin x :

a

Where y = \sin x is increasing most rapidly.

b

Where y = \sin x is decreasing most rapidly.

c

Where y = \sin x is stationary.

\frac{1}{2}π
\frac{3}{2}π
x
-1
1
y
8

Consider the graph of y = - \sin x which is the gradient function of y = \cos x. A number of points have been labelled on the graph.

Name the point on the gradient function that corresponds to the following locations on the graph of y = \cos x :

a

Where y = \cos x is increasing most rapidly.

b

Where y = \cos x is decreasing most rapidly.

c

Where y = \cos x is stationary.

\frac{1}{2}π
\frac{3}{2}π
x
-1
1
y
9

There is an expansion system in mathematics that allows a function to be written in terms of powers of x. The value of \sin x and \cos x, for any value of x, can be given by the expansions below:

\sin x = x - \dfrac{x^{3}}{3!} + \dfrac{x^{5}}{5!} - \dfrac{x^{7}}{7!} + \dfrac{x^{9}}{9!} - \ldots

\cos x = 1 - \dfrac{x^{2}}{2!} + \dfrac{x^{4}}{4!} - \dfrac{x^{6}}{6!} + \dfrac{x^{8}}{8!} - \ldots

Use the expansions to find:

a

\dfrac{d}{dx} \left(\sin x\right) in terms of x.

b

\dfrac{d}{dx} \left(\cos x\right) in terms of x.

c

Hence express the derivatives of \sin x and \cos x in simplest form.

10

Differentiate the following:

a
y=x^{3} \sin x
b
y=\dfrac{1}{\cos x}
c
y = \left(x^{4} + 3\right) \cos 5 x
d
y=\cos ^{2}\left(x\right)
e
y = \sin ^{6}\left( 3 x\right)
f
y=\dfrac{4 x}{\sin x}
11

Find y' for the function defined by x y = \sin 5 x.

Gradients and tangents
12

For each of the following curves and given points:

i

Find an expression for \dfrac{dy}{dx}.

ii

Find the exact value of the gradient of the curve at the given point.

a

y = \cos 3 x at x = \dfrac{\pi}{18}.

b

y = \cos 4 x at x =- \dfrac{\pi}{3}.

c
y = 6- \cos 3 x at x = \dfrac{\pi}{9}.
d

y = \sin 4 x at x = \dfrac{\pi}{16}.

13

Consider the function y = \sin 2 x + 4.

a

Differentiate y = \sin 2 x + 4.

b

Solve for the first positive value of x at which \dfrac{d y}{d x} = 1. Give your answer in radians.

c

State whether the following functions have the same gradient at x = \dfrac{\pi}{6}:

i
y = \cos 2 x
ii
y = \sin 2 x
iii
y = \cos \left(\dfrac{\pi}{2} - 2 x\right)
iv
y = \sin \left(\dfrac{\pi}{2} - 2 x\right)
14

Consider the function y = \cos 6 x. Find the equation of the tangent to the graph at x = \dfrac{\pi}{18}.

15

Consider the function f \left( x \right) = - 4 \cos 3 x.

Find \theta, the angle that the tangent at x = \dfrac{\pi}{12} makes with the positive x-axis. Round your answer to the nearest degree.

16

Consider the function f \left( x \right) = \cos 2 x - \sqrt{3} \sin 2 x and the first point to the right of the origin at which the curve intersects the x-axis.

Find \theta, the angle that the tangent makes with the positive x-axis at this point. Round your answer to the nearest degree.

17

For the function y = \sin x:

a

What is the equation of the tangent to the graph at each maximum?

b

What is the equation of the tangent to the graph at each minimum?

c

Find the equation of the tangent to the graph at x = \pi.

18

For the function y = 2 \cos x + 1:

a

What is the equation of the tangent to the graph at x = 0?

b

What is the equation of the tangent to the graph at each minimum?

c

Find the equation of the tangent to the graph at x = \dfrac{\pi}{2}.

19

Differentiate y = \sin( x\degree ).

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Outcomes

3.2.1.1

estimate the limit of 𝑎^(ℎ−1)/ℎ as ℎ→0 using technology, for various values of 𝑎>0

3.2.3.1

establish the formulas 𝑑/𝑑x sin(𝑥)=cos(𝑥), and 𝑑/𝑑x cos(𝑥)=− sin(𝑥) by numerical estimations of the limits and informal proofs based on geometric constructions

3.2.3.2

identify contexts suitable for modelling by trigonometric functions and their derivatives and use the model to solve practical problems; verify and evaluate the usefulness of the model using qualitative statements and quantitative analysis

3.2.4.1

select and apply the product rule, quotient rule and chain rule to differentiate functions; express derivatives in simplest and factorised form

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