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VCE 11 Methods 2023

7.09 Graphs of logarithmic functions

Worksheet
Graphs of logarithmic functions
1

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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2

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

a

Complete the following table of values:

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

Sketch a graph of the function.

c

State the equation of the vertical asymptote.

3

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.

4

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?

5

Consider the given graph of the logarithmic function y = \log_{a} x:

a

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

b

Which is a possible value for a:

\dfrac{2}{3} or \dfrac{3}{2} ?

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6

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

7

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.

8

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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9

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

a

y = k \log_{2} x

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b

y = 4 \log_{b} x

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c

y = \log_{4} x + c

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10

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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Transformations of logarithmic functions
11

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

a

Complete the table of values below:

x-8-4-2-1-\dfrac{1}{2}
f\left(x\right)=\log_2 \left( - x \right)
g\left(x\right)=\log_2 \left( - x \right) - 3
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

Determine whether each of the following features of the graph will remain unchanged after the given transformation:

i

The vertical asymptote.

ii

The general shape of the graph.

iii

The x-intercept.

iv

The domain.

12

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

Determine whether each of the following features of the graph will remain unchanged after the given transformation:

i

The vertical asymptote.

ii

The general shape of the graph.

iii

The x-intercept.

iv

The range.

13

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.

c

y= \log_{2} x + 4.

14

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

15

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.

16

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 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)
17

Given that the graph of y = \log_{5} x has a vertical asymptote at x = 0, state the equation of the asymptote of y = 3 \log_{5} x.

18

Given the graph of y = \log_{8} \left( - x \right), sketch the graph of y = 3 \log_{8} \left( - x \right).

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19

Given the graph of y = \log_{2} x, sketch the graph of the following functions:

a
y = \dfrac{1}{3} \log_{2} x
b
y = - \dfrac{1}{2} \log_{2} x
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Outcomes

U1.AoS1.2

qualitative interpretation of features of graphs of functions, including those of real data not explicitly represented by a rule, with approximate location of any intercepts, stationary points and points of inflection

U2.AoS1.19

sketch by hand the unit circle, graphs of the sine, cosine and exponential functions, and simple transformations of these to the form Af(bx)+c , sketch by hand graphs of log_a(x) and the tangent function, and identify any vertical or horizontal asymptotes

U2.AoS1.20

draw graphs of circular, exponential and simple logarithmic functions over a given domain and identify and discuss key features and properties of these graphs, including any vertical or horizontal asymptotes

U2.AoS1.8

logarithmic functions of the form f(x)=log_a(x), and their graphs and as the inverse function of y=a^x, including the relationships a^log_a(x)=x and log_a(a^x)=x

U2.AoS1.17

the key features and properties of the exponential functions, logarithmic functions and their graphs, including any vertical or horizontal asymptotes

U2.AoS1.16

characteristics of data which suggest the use of sine, cosine, exponential or logarithmic functions as an appropriate type of model for a given context

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