# Quick question on inverse functions

• September 2nd 2008, 05:42 PM
cb220
Quick question on inverse functions
Hi, just starting to recall how to grab the inverse of a function from last year. I just encountered a question that didn't say if it wanted the answer in x= or y=. Is it safe to assume that if the question does not specify that the answer should be written in x= ?

Simple example:

A function f is defined by y=2x+1. What is the equation of the inverse of f?

This question doesn't seem to specify whether to write it in x= or y= so I would assume the answer to be x=2y+1.

Or does something in that question tell me to write it as 'x=' without my realizing it?

Any help is appreciated, thanks.

EDIT: Just occurred to me it might be helpful if I show what I mean by 'y=', I'll just put the above equation into 'y=' to hopefully make more sense of what I'm getting at with the 'x=' 'y=' bit.

y=(x-1)/2

(I think?)
• September 2nd 2008, 06:08 PM
skeeter
you are correct ...

if the original function is y = 2x+1, then the inverse is
x = 2y+1 or y = (x-1)/2.

the last two equations are equivalent ... the last y represents $f^{-1}$.
• September 2nd 2008, 06:17 PM
cb220
I see, thank you :)