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iGCSE (2021 Edition)

21.06 Exponential functions (Extended)

Worksheet
Exponential graphs
1

State whether the following graphs show an exponential function:

a
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b
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c
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d
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e
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2

Consider the graphs of the two exponential functions A and B:

One of the graphs is of y = 3^{x} and the other graph is of y = 6^{x}. Which is the graph of y = 3^{x}?

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y
3

Consider the graphs of the two exponential functions R and S:

a

One of the graphs is of y = 3^{x} and the other graph is of y = 5^{x}. Which is the graph of y = 5^{x}?

b

Which function has its graph below that of the other when x < 0? Explain your answer.

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y
4

Determine whether following are increasing or decreasing exponential functions:

a

y = 2^{x}

b

y = 2^{-x}

Increasing exponential graphs
5

Consider the expression y = 4^{x}.

i

Complete the table of values:

x-3-2-10123
y
ii

Sketch the graph.

iii

Describe what happens to the y-values as x increases.

iv

Describe what happens to the y-values as x decreases.

v

Does the curve cross the x-axis?

vi

At what value of y does the graph cross the y-axis?

g

Use your graph to approximate the solution of the equation 4^x=3.

6

For each of the following functions:

i

Find the y-value of the y-intercept of the curve.

ii

Complete the table of values:

x-3-2-10123
y
iii

Find the horizontal asymptote of the curve.

iv

Sketch the graph.

a
y = 5^{x}
b
y = 10^{x}
c
y = 2^{x}
7

Consider the expression y = 10^{x}.

i

Can the value of y ever be negative?

ii

Can the value of y ever be equal to 0?

iii

As the values of x get larger and larger, what value does y approach?

iv

As the values of x get smaller and smaller, what value does y approach?

v

Find the y-value of the y-intercept of the curve.

vi

How many x-intercepts does the curve have?

vii

Sketch the graph.

h

Use your graph to approximate the solution of the equation 10^x=2.

8

Consider the exponentials y = 2^{x} and y = 3^{x}:

a

Find the horizontal asymptote of each curve:

i
y = 2^{x}
ii

y = 3^{x}

b

Complete a table of values for each exponetial:

x-3-2-10123
y
i
y = 2^{x}
ii

y = 3^{x}

c

Sketch the graphs of y = 2^{x} and y = 3^{x} on the same set of axes.

d

Find the coordinates of the point at which the two graphs intersect.

Decreasing exponential graphs
9

Consider the two equations y = 5^{ - x } and y = 6^{ - x }. Which is decreasing more rapidly for \\x > 0?

10

Consider the expression y = 2^{ - x }.

i

Complete the table of values:

x-3-2-10123
y
ii

Sketch the graph.

iii

Describe what happens to the y-values as x increases.

iv

Describe what happens to the y-values as x decreases.

v

Does the curve cross the x-axis?

vi

At what value of y does the graph cross the y-axis?

g

Use your graph to approximate the solution of the equation 2^{-x}=5.

11

For each of the following functions:

i

Find the y-value of the y-intercept of the curve.

ii

Complete the table of values:

x-3-2-10123
y
iii

Find the horizontal asymptote of the curve.

iv

Sketch the graph.

a
y = 3^{ - x }
b
y = 4^{ - x }
c
y = 6^{ - x }
12

Consider the expression y = 9^{ - x }.

i

Can the value of y ever be negative?

ii

Can the value of y ever be equal to 0?

iii

As the values of x get larger and larger, what value does y approach?

iv

As the values of x get smaller and smaller, what value does y approach?

v

Find the y-value of the y-intercept of the curve.

vi

How many x-intercepts does the curve have?

vii

Sketch the graph.

h

Use your graph to approximate the solution of the equation 9^{-x}=5.

13

Consider the exponentials y = 5^{-x} and y = 8^{-x}:

a

Find the horizontal asymptote of each curve:

i
y = 5^{-x}
ii

y = 8^{-x}

b

Complete a table of values for each exponetial:

x-3-2-10123
y
i
y = 5^{-x}
ii

y = 8^{-x}

c

Sketch the graphs of y = 5^{-x} and y = 8^{-x} on the same set of axes.

d

Find the coordinates of the point at which the two graphs intersect.

Dilations and reflections
14

How could we use the graph of y = 7^{x} to draw the graph of y = 7^{ - x }?

15

Consider the graph of y = 2^{x}:

a

Describe a transformation of the graph of y = 2^{x} that would obtain y = 2^{ - x }.

b

Sketch the graph of y = 2^{ - x } on the same set of axes as y = 2^{x}.

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16

Consider the graph of y = 5^{x}:

a

Describe a transformation of the graph of y = 5^{x} that would obtain y = - 5^{x}.

b

Sketch the graph of y = - 5^{x} on the same set of axes as y = 5^{x}.

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17

Consider the graph of y = 8^{x}:

a

Describe a transformation of the graph of y = 8^{x} that would obtain y = - 8^{ - x }.

b

Sketch the graph of y = - 8^{ - x } on the same set of axes as y = 8^{x}

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18

Consider the graph of y = 6^{ - x }:

a

Describe a transformation of the graph of y = 6^{ - x } that would obtain y = - 6^{ - x }.

b

Sketch the graph of y = - 6^{ - x } on the same set of axes as y = 6^{ - x }.

c

Describe the graph of y = - 6^{ - x } as x increases.

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19

Of the two functions y = 4^{x} and y = \dfrac{4^{x}}{4}, which is increasing more rapidly for x > 0?

20

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

a

Find the y-value of the y-intercept of the curve.

b

Can the value of y ever be negative?

c

As x approaches infinity, what value does y approach?

d

Sketch the graph of y = 3 \left(4^{x}\right).

21

Consider the function y = 3 \times 2^{x}.

a

Find the value of y when x = 0.

b

Describe a transformation of the graph of y = 3 \times 2^{x} that would obtain \\ y = - 3 \times 2^{x}.

c

Sketch the graph of y = - 3 \times 2^{x} on the same set of axes as y = 3 \times 2^{x}.

d

The number of bacteria over time is to be modelled by an exponential function, with x representing time and y representing the number of bacteria.

If the bacteria are increasing, which function should be used?

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22

Consider the original graph y = 2^{x}. The function values of the graph are multiplied by 3 to form a new graph.

a

Complete the following table by finding the points on the new graph:

Point on original graph\left(-1,\dfrac{1}{2}\right)\left(0,1\right)\left(1,2\right)\left(2,4\right)
Point on new graph\left(-1,⬚ \right)\left(0,⬚\right)\left(1,⬚\right)\left(2,⬚\right)
b

Find the equation of the new graph.

c

Sketch the graphs of the original and new function on the same set of axes.

d

For positive x-values, is the graph of the new function above or below the graph of 2^{x}?

e

For negative x-values, is the graph of the new function above or below the graph of 2^{x}?

Translations
23

Consider the graph of y = 6^{x}:

a

Find the y-value of the y-intercept of y = 6^{x}.

b

Hence, find the y-value of the y-intercept of y = 6^{x} + 3.

c

Find the horizontal asymptote of y = 6^{x}.

d

Hence, find the horizontal asymptote of y = 6^{x} + 3.

24

Consider the graph of y = 2^{x}:

a

Describe the translation required to shift the graph of y = 2^{x} to obtain the graph of y = 2^{x} - 5.

b

Sketch the graph of y = 2^{x} - 5 on the same set of axes as y = 2^{x}.

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25

Consider the graph of y = 3^{x}:

a

Describe the translation required to shift the graph of y = 3^{x} to obtain the graph of y = 3^{x} + 1.

b

Sketch the graph of y = 3^{x} + 1 on the same set of axes as y = 3^{x}.

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26

Consider the graph of y = 3^{ - x }:

a

Describe the translation required to shift the graph of y = 3^{ - x } to obtain the graph of y = 3^{ - x } + 5.

b

Sketch the graph of y = 3^{ - x } + 5 on the same set of axes as y = 3^{ - x }.

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27

Consider the graph of y = 3^{x}:

a

Describe the translation required to shift the graph of y = 3^{ x } to obtain the graph of y = 3^{ x -2} .

b

Sketch the graph of y = 3^{ x -2} on the same set of axes as y = 3^{ x }.

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28

Consider the graph of y = 2^{x}:

a

Describe the translation required to shift the graph of y = 2^{ x } to obtain the graph of y = 2^{ x +3} .

b

Sketch the graph of y = 2^{ x +3} on the same set of axes as y = 2^{ x }.

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29

Consider the graph of y = 4^{-x}:

a

Describe the translation required to shift the graph of y = 4^{ -x } to obtain the graph of y = 4^{ -x +1} .

b

Sketch the graph of y = 4^{ -x +1} on the same set of axes as y = 4^{ - x }.

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30

Consider the graph of y = 6^{-x}:

a

Describe the translation required to shift the graph of y = 6^{ -x } to obtain the graph of y = 6^{ -x -4} .

b

Sketch the graph of y = 6^{ -x -4} on the same set of axes as y = 6^{ - x }.

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31

State the new equation when the graph of y = 2^{x} is moved down by 9 units.

32

State the new equation when the graph of y = 12^{x} is moved left by 6 units.

33

State the new equation when the graph of y = 3^{-x} is moved right by 2 units and down by 7 units.

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Outcomes

0580C2.11C

Construct tables of values for functions of the form a^x (x =ΜΈ 0), where a and b are integer constants. Draw and interpret these graphs. Recognise, sketch and interpret graphs of functions

0580E2.11A

Construct tables of values and draw graphs for functions of the form ax^n (and simple sums of these) and functions of the form ab^x + c. Solve associated equations approximately, including finding and interpreting roots by graphical methods. Recognise, sketch and interpret graphs of functions.

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