Let f (x) = 3 + x + ln(x − 8 ), x > 8.

(a) Find f^-1(12)
(b) Find f^-( f (15))

2. ## Re: Can anyone tell me how i can go about this problem? inverse function related

Originally Posted by amramr
Let f (x) = 3 + x + ln(x − 8 ), x > 8.

(a) Find f^-1(12)
(b) Find f^-( f (15))
(a) by observation, $f(9) = 12 \implies f^{-1}(12) = 9$

(b) note ...

the function $f$ maps $x \to f(x) \implies$ the inverse function $f^{-1}$ maps $f(x) \to x$

so, $f^{-1}[f(15)] = \, ?$