Posted by **Janie** on Tuesday, August 24, 2010 at 2:00am.

if f(x) = (x/7)-3 find f^-1(x)

I'm completely lost! Help

- CONFUSED~MATH -
**drwls**, Tuesday, August 24, 2010 at 2:09am
The inverse function f^-1(x) gives you back x when you input y = f(x) as the independent variable.

Start with y = (x/7)-3

y + 3 = x/7

x = 7y + 21

Since you are using x as the independent variable of the inverse function, you have to switch x and y in the equation above.

The inverse function is therefore

f^-1(x) = 7x + 21

Check: Use (7x +21) as "x" in the f(x) equation, and you get x back.

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