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VCE 12 Methods 2023

2.05 Inverse functions

Worksheet
Inverse functions
1

For each function drawn below, determine if it has an inverse:

a
-8
-6
-4
-2
2
4
6
8
x
-8
-6
-4
-2
2
4
6
8
y
b
-8
-6
-4
-2
2
4
6
8
x
-8
-6
-4
-2
2
4
6
8
y
c
-8
-6
-4
-2
2
4
6
8
x
-8
-6
-4
-2
2
4
6
8
y
d
-8
-6
-4
-2
2
4
6
8
x
-8
-6
-4
-2
2
4
6
8
y
2

Determine whether the following functions have an inverse function:

a

\dfrac{7}{x}

b

\sqrt{7 - x^{2}}

c

\sqrt{x} + 7

d

1 - 7 x

e

7^{x}

f

4 x^{3} + 8

g

\sqrt{4 + x}

h

- \dfrac{1}{7} x^{2}

3

For each of the following functions:

i

Sketch the graph of f \left( x \right).

ii

State whether the function f \left( x \right) is one-to-one.

iii

State whether an inverse function exists.

a

f \left( x \right) = x + 5

b

f \left( x \right) = \dfrac{2 x + 3}{2}

c

f \left( x \right) = \left(x - 2\right) \left(x + 3\right)

d

f \left( x \right) = x^{2}-1

e

f \left( x \right) = \left(x - 5\right)^{3}

f

f \left( x \right) = \dfrac{1}{8 - x} for x \neq 8

4

Consider the function f \left( x \right) = \dfrac{4}{x + 4}.

a

Sketch the graph of the function.

b

Is the function a one-to-one function?

c

Find an expression for the inverse function f^{ - 1 } \left(x\right).

5

For each of the following functions, find an expression for the inverse function \\ y = f^{ - 1 } \left(x\right):

a

f \left( x \right) = - \dfrac{4}{x}

-8
-6
-4
-2
2
4
6
8
x
-8
-6
-4
-2
2
4
6
8
y
b

f \left( x \right) = \sqrt[3]{x} + 5

-8
-6
-4
-2
2
4
6
8
x
-8
-6
-4
-2
2
4
6
8
y
6

For each of the following functions, find an expression for the inverse function y = f^{ - 1 } \left(x\right):

a

f \left( x \right) = 7 x - 8

b

f \left( x \right) = \dfrac{4 x}{3} - 5

c

f \left( x \right) = 6 x^{3}

d

f \left( x \right) = \sqrt[3]{x - 2}

e

f \left( x \right) = \dfrac{8}{x - 9} + 5

f

f \left( x \right) = \left(x - 4\right)^{3} + 3

g

f \left( x \right) = \dfrac{8}{5 x + 3}

h

f \left( x \right) = \dfrac{7}{\left(x + 8\right)^{3}} - 3

i

f \left( x \right) = 4 \left( 9 x - 2\right)^{3} - 7

Restricting the domain
7

For many functions, we can determine an inverse relation by first breaking up the original function into parts that are one-to-one, and then finding the inverse of each part separately.

a

Complete the function below to break f \left( x \right) = \left(x - 2\right)^{2} - 6 into two one-to-one functions that have the same rule as f \left( x \right).

f(x) = \begin{cases} \left( x - 2 \right)^2 - 6, & x \lt ⬚ \\ \left( x - 2 \right)^2 - 6, & x \geq ⬚ \end{cases}

b

Consider the graph of y = g \left( x \right) shown:

-6
-5
-4
-3
-2
-1
1
2
3
4
5
6
7
8
9
10
11
x
-5
-4
-3
-2
-1
1
2
3
4
5
y

Complete the function below to break the graph of y = g \left( x \right) into three one-to-one functions that have the same rule as g \left( x \right).

f(x) = \begin{cases} g \left( x \right), & x \leq ⬚ \\ g \left( x \right), & ⬚ \lt x \lt ⬚ \\ g \left( x \right), & x \geq ⬚ \end{cases}

8

Find an appropriate restricted domain for the function f \left( x \right) = \left(x - 7\right)^{2} + 12 to have an inverse.

9

Consider the function f \left( x \right) = \left(x - 4\right)^{2} - 6 on the restricted domain \left[4, \infty\right).

a

Find the inverse function f^{ - 1 } \left(x\right) for f \left( x \right) on the restricted domain.

b

State the domain and range of f^{-1} (x).

10

Consider the function f \left( x \right) = \left(x + 2\right)^{2} - 9.

a

State the domain restriction corresponding to the right half of the parabola described by f \left( x \right), such that the restricted parabola is a one-to-one function.

b

Find the inverse function f^{ - 1 } \left(x\right) for f \left( x \right) on the restricted domain found in part (a).

c

State the domain and range of f^{-1} (x).

11

Consider the function f \left( x \right) = \left(x + 4\right)^{4}.

a

State the domain restriction corresponding to the right half of the quartic defined by f \left( x \right), such that the restricted quartic is a one-to-one function.

b

Find the inverse function f^{ - 1 } \left(x\right) for f \left( x \right) on the restricted domain found in part (a).

c

State the domain and range of f^{-1} (x).

12

Consider the function f \left( x \right) = - \left(x - 5\right)^{2}.

a

State the domain restriction corresponding to the left half of the parabola defined by f \left( x \right), such that the restricted parabola is a one-to-one function.

b

Find the inverse function f^{ - 1 } \left(x\right) for f \left( x \right) on the restricted domain found in part (a).

c

State the domain and range of f^{-1} (x).

13

Consider the function f \left( x \right) = x^{2} + 10 x + 23.

a

Complete the square for f \left( x \right) to write the function in turning point form.

b

State the domain restriction that defines the right half of this function, making it one-to-one.

c

Find the inverse function f^{ - 1 } \left(x\right) for f \left( x \right) on the restricted domain found in part (b).

d

State the domain and range of f^{ - 1 } \left(x\right).

14

Consider the function f \left( x \right) = x^{2} + 4 x + 3.

a

Factorise f \left( x \right) fully.

b

Find the axis of symmetry of f \left( x \right).

c

State the domain restriction that defines the right half of this function, making it one-to-one.

d

Find the inverse function f^{ - 1 } \left(x\right) for f \left( x \right) on the restricted domain found in part (c).

e

State the domain and range of f^{ - 1 } \left(x\right).

15

The inverse of a function f \left( x \right) is f^{ - 1 } \left(x\right) = \sqrt{8 - x}.

a

State the domain and range of f^{ - 1 } \left(x\right).

b

If f^{ - 1 } \left(x\right) is the inverse of f \left( x \right), find f \left( x \right).

c

State the domain restriction on f \left( x \right).

d

What do you notice about the domain and range of f \left( x \right) and f^{ - 1 } \left(x\right)?

16

Consider the function f \left( x \right) = \sqrt{x - 5} + 8.

a

State the domain and range of f \left( x \right).

b

Is the function f \left( x \right) a one-to-one function?

c

Find the inverse function f^{ - 1 } \left(x\right).

d

Given that f \left( x \right) is only half a parabola, what must be the domain restriction on f^{ - 1 } \left(x\right)?

e

What do you notice about the domain and range of f \left( x \right) and f^{ - 1 } \left(x\right)?

17

Consider the function f \left( x \right) = \left(x - a\right)^{4} + b.

a

State the largest domain and range of f \left( x \right) in terms of a and b that would make f \left( x \right) invertible.

b

Find the inverse function f^{ - 1 } \left(x\right).

c

State the domain and range of f^{ - 1 } \left(x\right) in terms of a and b.

18

Consider the function f \left( x \right) = - \left(x - a\right)^{2} - a.

a

What would be the domain restriction on f \left( x \right) in terms of a if we only want to keep the right half of the parabola?

b

Find the inverse function f^{ - 1 } \left(x\right).

19

The largest domain over which the function f \left( x \right) = x^{2} + b x + c has an inverse is \left[3, \infty\right). The domain of the inverse function f^{ - 1 } \left(x\right) is \left[ - 2 , \infty\right).

a

Find the value of b.

b

Find the value of c.

Applications
20

An encryption tool takes in a 10-digit code, n, and puts it into the formula K = \left(n - a\right)^{4} + b to create an encrypted key, K. It is important that when we try to get the code back from the key there is only one possible value for n.

Determine whether the following restrictions should be imposed to ensure the correct code is returned:

a

K > b

b

n > a

c

n > b

d

K > a

21

A particle is moving along a straight line path. After t seconds, its velocity is given by the equation v = \left( 96 t - 80\right)^{2}.

a

Solve for the time t at which the particle comes to rest.

b

Determine the equation for time, t, in terms of velocity, v, that represents the motion of the particle before it has come to rest.

22

The tax on a new tablet is 7\% of the advertised price, A.

a

Determine the equation for the total cost T as a function of the advertised price A.

b

Hence, express the advertised price A as a function of the total cost T.

23

The function t = \sqrt{\dfrac{d}{4.9}} can be used to find the number of seconds it takes for an object in Earth's atmosphere to fall d metres.

a

State the function for d in terms of t.

b

Hence, find the distance a skydiver has fallen 5 seconds after jumping out of a plane.

24

The function T = 2 \pi \sqrt{\dfrac{l}{9.8}} can be used to find the period T of a simple pendulum of length l metres.

a

Express the length l as a function of the period T.

b

Hence, find the length of a pendulum whose period is 1.5 seconds. Round your answer to one decimal place.

25

The per capita \text{CO}_2 emissions of Norway have been recorded since 1950, and the tonnes per capita emissions M, at a time t years after 1950, can be approximated by the model M = 2.95 \sqrt{t} + 7.8.

a

Determine the per capita \text{CO}_2 emissions at the time when recording started.

b

Express t as a function of M.

c

Hence, find the number of years it took for the per capita emissions of 1950 to double. Round your answer to one decimal place.

26

The function d(t) = 120 - 4.9 t^{2} can be used to find the distance d that an object dropped from a height of 120 \text{ m} has fallen after t seconds.

a

Is the function one-to-one?

b

Find the inverse function, t(d).

c

Prove that d \left( t \left(d\right)\right) = d.

d

Prove that t \left( d \left(t\right)\right) = t.

e

Are d and t inverse functions?

f

Determine how long it will take an object to fall 41.6 \text{ m} when dropped from a height of 120 \text{ m}.

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Outcomes

U34.AoS1.3

transformation from y=f(x) to y=A(f(n(x+b))+c and f is one of the functions specified above, and the inverse transformation

U34.AoS1.4

the relation between the graph of an original function and the graph of a corresponding transformed function (including families of transformed functions for a single transformation parameter)

U34.AoS1.11

the concept of an inverse function, connection between domain and range of the original function and its inverse relation and the conditions for existence of an inverse function, including the form of the graph of the inverse function for specified functions

U34.AoS1.16

find the rule of an inverse function and give its domain and range

U34.AoS2.2

functions and their inverses, including conditions for the existence of an inverse function, and use of inverse functions to solve equations involving exponential, logarithmic, circular and power functions

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