Find The Inverse Function Values from Graphs
Questions With Detailed Solutions

How to find the values of the inverse of a function from its graph? Grade 11 examples and questions are presented along with their detailed solutions and explanations.


Example

Use the graph of f shown below to find the following,if possible,:
a) f -1(5) , b) f -1(0) , c) f -1(- 3) , d) f -1( - 4) , e) f -1(- 5)

function given by graph

Figure 1. Graph of a function, example 1

Solution


a) According to the the definition of the inverse function
a = f -1(5)     if and only if     5 = f(a)
Meaning that a is the value of x such f(x) = 5.
Using the graph below: start from y = 5 on the y-axis and draw a horizontal line to the graph of f then go down to the x axis to find x = 3. Therefore f(3) = 5. Hence a = 3 and therefore f -1(5) = 3
function given by graph, solution

Figure 2. Graph of a function, example 1, solution
b) a = f -1(0)     if and only if     f(a) = 0
According to the graph shown, f(2) = 0 and therefore f -1(0) = 2.
c) a = f -1(- 3)     if and only if     f(a) = - 3
The value of x for which f(x) = - 3 is equal to 1 and therefore f -1(- 3) = 1
d) a = f -1(- 4)     if and only if     f(a) = - 4
The value of x for which f(x) = - 4 is 0 and therefore f -1(- 4) = 0.
e) a = f -1(- 5)     if and only if     f(a) = - 5
According to the graph of f, there is no value of x for which f(x) = - 5 and therefore f -1(- 5) is undefined.

More Questions with Solutions

Question 1 - Use the graph of function g shown below to find the following if possible:
a) g -1(6) , b) g -1(0) , c) g -1(- 2) , d) g -1(4) , e) g -1(8)
function g given by its graph

Figure 3. Graph of function g, question 1

Question 2 - Use the graph of function h shown below to find the following if possible:
a) h -1(1) , b) h -1(0) , c) h -1(- 1) , d) h -1(2)

.

function h given by its graph

Figure 4. Graph of function h, question 2

Solutions to the Above Questions

Solution to Question 1
a) According to the the definition of the inverse function:
a = g -1(6)     if and only if     6 = g(a)
Meaning that a is the value of x such g(x) = 6.
Using the graph below for x = 2, g(x) = 6. Hence a = 2 and therefore g -1(6) = 2

function given by graph solution.


b) a = g -1(0)     if and only if     g(a) = 0
According to the graph shown, g(- 1) = 0 and therefore g -1(0) = - 1.
c) a = g -1(- 2)     if and only if     g(a) = - 2
The value of x for which g(x) = - 2 is equal to - 2 and therefore g -1(- 2) = - 2
d) a = g -1(4)     if and only if     g(a) = 4
The value of x for which g(x) = 4 is 1 and therefore g -1(4) = 1.
e) a = g -1(8)     if and only if     g(a) = 8
According to the graph of g, there is no value of x for which g(x) = 8 and therefore g -1(8) is undefined.



Solution to Question 2
a) According to the the definition of the inverse function:
a = h -1(1)     if and only if     1 = h(a) ,
Meaning that a is the value of x such h(x) = 1.
According to the graph shown, h(0) = 1 and therefore h -1(1) = 0.
b) a = h -1(0)     if and only if     h(a) = 0
According to the graph shown, h(π/2) = 0 and therefore h -1(0) = π/2.
c) a = h -1(-1)     if and only if     h(a) = -1
According to the graph shown, h(π) = - 1 and therefore h -1(-1) = π.
d) a = h -1(2)     if and only if     h(a) = 2
According to the graph shown, there is no value of x for which h(x) = 2 and therefore h -1(2) is undefined.

More References and links

Find Inverse Function from Table
Inverse Function
Find Inverse Function (1) - Tutorial
Middle School Maths (Grades 6, 7, 8, 9) - Free Questions and Problems With Answers
High School Maths (Grades 10, 11 and 12) - Free Questions and Problems With Answers
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