Math CentralQuandaries & Queries


Question from Peter, a student:

how do you do functions like f^-1(3) when f(x)=2x-1?


Let me try this one

What is g-1( 13) if g(x) = 5x + 3?

Another way to ask this question is

What value of x gives g(x) = 13?

Sometimes you can easily see the answer.

Since g(x) = 5x + 3 you can see that when x = 2, g(x) = g(2) = 13.

Sometime you need to use algebra.

If g(x) = 13 the 5x + 3 = 13 and solve for x to find that x = 2.

Whichever method you use you see that g-1(13) = 2 since g(2) = 13.

I hope this helps,

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