precalculus word problem

[girlpower]

I am having a hard time with this problem:

If f (x)= 7x +2 and f-1 denotes the inverse function of f, then find f-1 (9).

 

[srmichael]

I am having a hard time with this problem:

If f (x)= 7x +2 and f-1 denotes the inverse function of f, then find f-1 (9).

Do you know the process of finding the inverse of a function?

 

[Novice]

I am having a hard time with this problem:

If f (x)= 7x +2 and f-1 denotes the inverse function of f, then find f-1 (9).

Let y=7x+2.
Make x the subject of formula, i.e. find x in terms of y, and guess what, you'll have the inverse function. Putting 9 in place of the independent variable, you will get the answer.

 

[MarkFL]

Another way to look at this is to let f(x) = 9, then solve for x. This will tell you what the inverse function evaluated at x = 9 is.

We may state:

\(\displaystyle f^{-1}(9)=x\)

Now take the function of both sides:

\(\displaystyle f(f^{-1}(9))=f(x)\)

\(\displaystyle 9=7x+2\)

Now solve for x.