Please help!
if f(x) and f^–1(x) are inverse functions of each other and f(x)=2x+5, what is f^-1(8)?
A. -1
B. 3/2
C. 41/8
D. 23

Question

Please help!
if f(x) and f^–1(x) are inverse functions of each other and f(x)=2x+5, what is f^-1(8)?
A. -1
B. 3/2
C. 41/8
D. 23

mathmale · Answer

You are given f(x)=2x+5.  Finding the inverse function of that is quite straightforward; why not do it now?  Then evaluate this inverse function for x=8.

An alternative approach follows:  If f(x)=2x+5=8, we say "(x,8) is a solution of 2x+5=8.  This being true, then (8,x) would be the solution to the inverse of function f(xc).

Try it.