Exercise 4 Page 123

To find the value of x that will make the function equal to 21, we will substitute 21 for f(x) in the given function rule. Then, we can solve for x.

f(x)=6x+9

Substitute

f(x)= 21

21=6x+9

SubEqn

LHS-9=RHS-9

12=6x

DivEqn

.LHS /6.=.RHS /6.

2=x

RearrangeEqn

Rearrange equation

x=2

When x=2, the function equals 21.

Checking Our Answer

Verifying Our Solution

We can verify our solution by substituting x=2 into the function and evaluating.

f(x)=6x+9

Substitute

x= 2

f( 2)=6( 2)+9

Multiply

Multiply

f(2)=12+9

AddTerms

Add terms

f(2)=21

When x=2, f(x)=21, so our solution is correct.