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VCE 12 Methods 2023

4.08 Transformations of logarithms

Worksheet
Describe transformations
1

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
-1
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-5
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b
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-5
-4
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c
-4
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-2
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d
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-4
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2

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.

3

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

4

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.

5

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

6

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)
7

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
8

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)?

9

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

10

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

11

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
12

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).

-1
1
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x
-5
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13

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).

-5
-4
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-2
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-4
-3
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y
14

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).

1
2
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x
-5
-4
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y
15

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).

1
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x
-4
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y
16

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).

1
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x
-2
-1
1
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y
17

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

a

y = k \log_{2} x

2
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-2
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y
b

y = \log_{4} x + c

-4
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18

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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19

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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20

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)
-1
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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.

21

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.

22

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.

23

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.

24

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
25

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)
26

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.

27

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.

28

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.

29

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).

30

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)
31

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)
32

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

33

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

U34.AoS1.14

identify key features and properties of the graph of a function or relation and draw the graphs of specified functions and relations, clearly identifying their key features and properties, including any vertical or horizontal asymptotes

U34.AoS1.18

sketch by hand graphs of polynomial functions up to degree 4; simple power functions, y=x^n where n in N, y=a^x, (using key points (-1, 1/a), (0,1), and (1,a); log x base e; log x base 10; and simple transformations of these

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