Question

If f(x) and f-1(x) are inverse functions of each other and f(x)=2x+5, what is f-1(8)?

Answer 1

For this case we have the following function:
 f (x) = 2x + 5
 Clearing x we have:
 2x = y - 5
 x = (y-5) / 2
 Rewriting:
 f (x) ^ - 1 = (x-5) / 2
 Evaluating x = 8:
 f (8) ^ - 1 = (8-5) / 2
 f (8) ^ - 1 = 3/2
 Answer:
 f (8) ^ - 1 = 3/2
 option 2

Answer 2

Answer:

3/2

Step-by-step explanation:

f(x)=2x+5

first find inverse (write it without f(x))

y = 2x +  5

x = 2y + 5  (swap the variables, now solve for y)

-  5      -5

x - 5 = 2y

/2         /2  (divide both sides by 2)

(x-5)/2 = y

so f-1(x) = (x-5)/2

f-1(8) = (8-5)/2

         = (3)/2

f-1(8) = 3/2