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6.05 Graphs of logarithms

Worksheet
Properties of logarithmic graphs
1

Consider the functions graphed below.

Which of these graphs represents a logarithmic function of the form y = \log_{a} \left(x\right)?

A
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B
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C
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D
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2

Consider the function f \left(x\right) = \log_{3} x.

a

Complete the table of coordinates for the given function.

PointABCDEFGH
Coordinate\left(\dfrac{1}{9}, ⬚ \right)\left(\dfrac{1}{3},⬚ \right)\left(1, ⬚\right)\left(3, ⬚\right)\left(9, ⬚\right)\left(⬚, 3\right)\left(⬚, 4\right)\left(⬚, 5\right)
b

Sketch the graph of f\left(x \right), clearly indicating the points C, D and E on the graph.

3

Consider the function y = \log_{2} x.

a

Complete the table of values for the function:

b

Sketch a graph of the function.

c

State the equation of the vertical asymptote.

x\dfrac{1}{2}12416
y
4

State whether the following elements are key features of the graph of y = \log_{2} x:

a

The y-intercept

b

A vertical asymptote

c

A horizontal asymptote

d

The x-intercept

e

A lower limiting value

f

An upper limiting value

5

Consider the function y = \log_{3} x.

a

Find the x-intercept.

b

Complete the table of values for \\y = \log_{3} x:

c

State the equation of the vertical asymptote.

d

Sketch the graph of y = \log_{3} x.

e

Is the function increasing or decreasing?

x\dfrac{1}{3}139
y
6

Consider the function y = \log_{4} x and its given graph:

a

Complete the following table of values:

x\dfrac{1}{16}\dfrac{1}{4}416256
y
b

Find the x-intercept.

c

How many y-intercepts does the function have?

d

Find the x-value for which \log_{4} x = 1.

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7

Consider the given graph of f \left(x\right) = \log_{5} x.

Determine whether the following statements are true or false.

a

f \left(x\right) = \log_{5} x has no asymptotes.

b

f \left(x\right) = \log_{5} x has a vertical asymptote.

c

f \left(x\right) = \log_{5} x has a horizontal asymptote.

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8

Consider the following function y = \log_{3} x.

a

State the x-intercept of y = \log_{3} x.

b

What happens to the value of y = \log_{3} x as x gets larger?

c

What happens to the value of y = \log_{3} x as x gets smaller, approaching zero?

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9

Consider the function y = \log_{4} x.

a

Complete the table of values.

x\dfrac{1}{1024}\dfrac{1}{4}1416256
y
b

Is \log_{4} x an increasing or decreasing function?

c

Describe the behaviour of \log_{4} x as x approaches 0.

d

State the value of y when x = 0.

10

Consider the function y = \log_{a} x, where a is a value greater than 1.

a

For which of the following values of x will \log_{a} x be negative?

A

x = - 9

B

x = \dfrac{1}{9}

C

x = 9

D

\log_{a} x is never negative

b

For which of the following values of x will \log_{a} x be positive?

A

x = 5

B

x = - 5

C

x = \dfrac{1}{5}

D

\log_{a} x will never be positive

c

Is there a value that \log_{a} x will always be greater than?

d

Is there a value that \log_{a} x will always be less than?

Different Bases
11

Consider the functions y = \log_{2} x and y = \log_{3} x.

a

Sketch the two functions on the same set of axes.

b

Describe how the size of the base relates to the steepness of the graph.

12

Consider the graph of y = \log_{5} x.

Graph y = \log_{3} x on the same set of axes.

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13

Consider the graphs of y = \log_{4} x, y = \log_{25} x and y = \log_{100} x graphed on the same set of axes.

a

Which graph is on the top in the interval \left(1, \infty\right)?

b

Which graph is on the bottom in the interval \left(1, \infty\right)?

c

Which graph is on the top in the interval \left(0, 1\right)?

d

Which graph is on the bottom in the interval \left(0, 1\right)?

14

Consider the given graph of f \left( x \right) = \log_{k} x.

a

Determine the value of the base k.

b

Hence, state the equation of f \left( x \right).

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Inverse functions
15

The functions y = 3^{x} and y = \log_{3} x have been graphed on the same set of axes.

a

State the domain of y = 3^{x}.

b

State the range of y = 3^{x}.

c

State the domain of y = \log_{3} x.

d

State the range of y = \log_{3} x.

e

Describe the relationship between the two functions.

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16

Consider the function y = \log_{2} x.

a

Complete the table of values for \\y = \log_{2} x:

x1248
y
b

Hence create a table of values for the inverse function of y = \log_{2} x.

x
y
c

Hence sketch the graph of y = \log_{2} x and its inverse function on the same set of coordinate axes, clearly indicating the points found in parts (a) and (b).

d

Determine the equation of the inverse function of y = \log_{2} x.

17

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

a

Graph F \left( x \right), the line y=x and the inverse to F \left( x \right) on the same set of axes.

b

What type of function is the inverse function of F \left( x \right)?

c

Hence, state the equation of the inverse function.

Describe transformations
18

For each of the following graphs of f \left( x \right) = \log x and g \left( x \right):

i

Describe the transformation applied to f \left( x \right) to obtain g \left( x \right).

ii

Hence, state the equation of g \left( x \right).

a
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19

The graph of y = \log_{6} x is transformed to create the graph of y = \log_{6} x + 4. Describe the tranformation that could achieve this.

20

If the function f \left( x \right) = \log_{3} x is translated 5 units to the right, state the equation of the resulting function.

21

Describe the transformation required to change the graph of g \left( x \right) into f \left( x \right) for each of the following:

a

g \left( x \right) = \log_{3} x into f \left( x \right) = \log_{3} x + k, where k > 0.

b

g \left( x \right) = \log_{3} x into f \left( x \right) = \log_{3} x + k, where k < 0.

c

g \left( x \right) = \log_{10} x into f \left( x \right) = \log_{10} \left(x - h\right), for h > 0.

d

g \left( x \right) = \log_{10} x into f \left( x \right) = \log_{10} \left(x - h\right), for h < 0.

e

g \left( x \right) = \log_{10} x into f \left( x \right) = a \log_{10} x, where a > 1.

f

g \left( x \right) = \log_{2} x into f \left( x \right) = a \log_{2} x, where 0 < a < 1.

22

Describe the transformation of g \left( x \right) = a \log_{10} x, to obtain f \left( x \right) = - a \log_{10} x.

23

Consider the graph of y = \log_{6} x which has a vertical asymptote at x = 0. This graph is transformed to give each of the new functions below. State the equation of the vertical asymptote for each new graph:

a
y = \log_{6} x - 7
b
y = \log_{6} x +2
c
y = 3\log_{6} x
d
y = \log_{6} \left(x - 2\right)
24

The graph of y = \log_{4} x has a vertical asymptote at x = 0. By considering the transformations that have taken place, state the equation of the vertical asymptote of the following functions:

a

y = 2 \log_{4} x - 4

b

y = 2 \log_{4} x

c

y = \log_{4} \left(x - 5\right)

d

y = - \log_{4} x

e

y = \log_{4} \left(x + 3\right) - 2

f
y = 3 \log_{4} x + 2
25

Consider the functions f \left( x \right) = \log_{2} x + \log_{2} \left( 3 x - 4\right) and g \left( x \right) = \log_{2} \left( 4 x - 4\right).

a

Evaluate f \left( 2 \right).

b

Evaluate g \left( 2 \right).

c

Is f \left( x \right) = g \left( x \right)?

26

State the domain for each of the following functions:

a

y = 5 \log_{5} x - 3

b

y = \log_{3} \left(x + 5\right) - 4

27

For any logarithmic function of the form y = a \log_{b} \left(x - h\right) + k, state the range of the function.

28

A logarithmic function of the form f \left( x \right) = \log_{3} \left(x - h\right) is used to generate the following table of values:

a

State the exact function used.

b

Hence, determine the value of f \left( 2.5 \right). Round your answer to three decimal places.

x351129
f\left(x\right) 0123
29

Consider the following graph of y = f \left( x \right):

a

When x = 1, state the value of y.

b

Describe the transformation that has been performed on the the graph of \\y = \log_{k} x to obtain the graph of f \left( x \right).

c

Hence, state the equation for f \left( x \right).

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30

Consider the following graph of y=f \left( x \right):

a

Write down the equation of the vertical asymptote of f \left( x \right).

b

Describe the transformation that has been performed on the the graph of \\y = \log_{k} x to obtain the graph of f \left( x \right).

c

Hence, state the equation for f \left( x \right).

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31

The graph of y=f \left( x \right) shown is a transformation of y = \log_{5} x.

a

Describe the transformation that has been performed on the graph of \\y = \log_{5} x to obtain f \left( x \right).

b

Hence, state the equation for f \left( x \right).

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32

Consider the following graph of y = f \left( x \right):

a

When f \left( x \right) = 0, state the value of x.

b

Describe the transformation that has been performed on the the graph of \\y = \log_{k} x to obtain the graph of f \left( x \right).

c

Hence, state the equation of f \left( x \right).

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33

The graph of y=f \left( x \right) shown is a transformation of y = \log_{3} x.

a

Describe the transformation that has been performed on the graph of \\y = \log_{3} x to obtain f \left( x \right).

b

Hence, state the equation of f \left( x \right).

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34

Find the equation of each of the following functions, given it is of the stated form:

a

y = k \log_{2} x

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b

y = \log_{4} x + c

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35

The function graphed has an equation of the form y = k \log_{2} x + c and passes through points A\left(4,11\right) and B\left(8,15\right):

a

Use the given points to form two equations relating c and k.

b

Hence, find the values of c and k.

c

State the equation of the function.

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36

Consider the functions graphed below:

Which of these graphs represents a logarithmic function of the form y = -\log_{a} \left(x\right)?

A
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37

Consider the graphs of the functions

  • y = \log_{2} x

  • y = \log_{2} x + 5

  • y = 5 \log_{2} x

graphed on the same coordinate axes.

a

Find the value of each function when x = 4:

i
f(4)
ii
h(4)
iii
g(4)
b

Match each function to its correct equation:

i
f\left(x \right)
ii
h\left(x \right)
iii
g\left(x \right)
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c

Describe the relationship between the values of the function f \left( x \right) and the function h \left( x \right), for very large values of x.

d

Describe the relationship between the values of the function f \left( x \right) and the function g \left( x \right), for very large values of x.

38

Consider the function f \left( x \right) = \log_{4} \left(k x\right) + 1. Solve for the value of k for which f \left( 4 \right) = 3.

39

Consider the function f \left( x \right) = \log_{2} 8 x.

a

Rewrite \log_{2} 8 x as a sum of two terms.

b

Hence describe how the graph of y = f \left( x \right) can be obtained from the graph of \\g \left( x \right) = \log_{2} x.

40

Consider the function f \left( x \right) = \log_{3} \left(\dfrac{x}{9}\right).

a

Rewrite \log_{3} \left(\dfrac{x}{9}\right) as a difference of two terms.

b

Hence describe how the graph of y = f \left( x \right) can be obtained from the graph of \\g \left( x \right) = \log_{3} x.

41

Consider the function f \left( x \right) = \log \left( 100 x - 500\right).

a

Rewrite \log \left( 100 x - 500\right) as a sum of two terms.

b

Hence describe how the graph of y = f \left( x \right) can be obtained from the graph of \\g \left( x \right) = \log x.

Graph logarithmic functions
42

Consider the function f \left(x \right) = \log_{3} x - 1.

a

Solve for the x-intercept.

b

Complete the table of values.

c

State the equation of the vertical asymptote.

d

Hence sketch the graph of f \left(x \right).

x\dfrac{1}{3}139
f \left(x \right)
43

Consider the functions f\left(x\right) = \log_{2} x and g\left(x\right) = \log_{2} x + 2.

a

Complete the table of values below:

x\dfrac{1}{2}1248
f\left(x\right)=\log_2 x
g\left(x\right)=\log_2 x + 2
b

Sketch the graphs of y = f\left(x\right) and y = g\left(x\right) on the same set of axes.

c

Describe a transformation that can be used to obtain g \left(x\right) from f \left(x\right).

d

State whether the following features of the graph of f \left(x\right) will remain unchanged after the transformation to g \left(x\right):

i

The vertical asymptote.

ii

The general shape of the graph.

iii

The x-intercept.

iv

The range.

44

Sketch the graph of the following functions:

a
y = \log_{3} x translated 2 units up.
b

y = \log_{3} x translated 4 units down.

45

For each of the following functions:

i

State the equation of the function after it has been translated.

ii

Sketch the translated graph.

a

y = \log_{5} x translated downwards by 2 units.

b

y = \log_{3} \left( - x \right) translated upwards by 2 units.

46

Consider the function f \left( x \right) = \log_{3} \left(x - 4\right).

a

State the equation of the vertical asymptote of f \left( x \right).

b

State the coordinates of the x-intercept of the function.

c

Determine the exact value of f \left( 7 \right).

d

Sketch a graph of f \left( x \right) = \log_{3} \left(x - 4\right).

47

Consider the function f \left(x\right) = - \log_{3} x.

a

Solve for the x-intercept.

b

Complete the table of values.

c

State the equation of the vertical asymptote.

d

Sketch the graph of f \left(x\right) = - \log_{3} x.

x\dfrac{1}{3}139
f \left(x\right)
48

Consider the function f \left(x\right) = - 3 \log_{5} x.

a

Solve for the x-intercept.

b

Complete the table of values.

c

State the equation of the vertical asymptote.

d

Sketch the graph of f \left(x\right) = - 3 \log_{5} x.

x\dfrac{1}{5}1525
f \left(x\right)
49

For each of the following functions:

i

Solve for the x-intercept.

ii

Complete the table of values.

iii

State the equation of the vertical asymptote.

iv

Sketch the graph of the function.

x\dfrac{1}{2}124
f \left(x\right)
a

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

b

f \left(x\right) = 3 \log_{2} x - 6

c

f \left(x\right) = - \log_{2} x + 2

d

f \left(x\right) = - 2 \log_{2} x + 2

50

For each of the following functions:

i

Solve for the x-intercept.

ii

State the equation of the vertical asymptote.

iii

Sketch the graph of the function.

a

f \left(x\right) = 4 \log_{2} \left(x - 7\right)

b

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

c

f \left(x\right) = \log_{2} \left(x - 1\right) - 4

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Outcomes

ACMMM156

recognise the qualitative features of the graph of y=log_a ⁡x (a>1) including asymptotes, and of its translations y=log_a ⁡x + b and y=log_a ⁡(x+c)

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