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

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

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