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

3/2

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

Answer 2

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