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VCE 12 Methods 2023

4.07 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
-5
5
x
-5
5
y
B
-5
5
x
-5
5
y
C
-5
5
x
-5
5
y
D
-5
5
x
-5
5
y
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.

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

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

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

-1
1
2
3
4
5
6
7
8
9
x
-5
-4
-3
-2
-1
1
2
3
4
5
y
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).

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

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

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Outcomes

U34.AoS1.2

graphs of the following functions: power functions, y=x^n; exponential functions, y=a^x, in particular y = e^x ; logarithmic functions, y = log_e(x) and y=log_10(x) ; and circular functions, 𝑦 = sin(𝑥) , 𝑦 = cos (𝑥) and 𝑦 = tan(𝑥) and their key features

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.AoS1.11

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.AoS1.18

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

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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