# Math Help - functions

1. ## functions

Let f(x) the function defined below, where -1 < x < 1.

a) Find f -1(7).

(b) Find f(f -1(8)).

I'm having a tough time finding the inverse.

2. Originally Posted by leftyguitarjoe
Let f(x) the function defined below, where -1 < x < 1.

a) Find f -1(7).
Find x such that :
$7=7+x^2+\tan\left(\frac{\pi x}{2}\right)$

One advice : $x^2 \ge 0$ and since $-1, $-\frac \pi 2 < \underbrace{\frac{\pi x}{2}}_{t} < \frac \pi 2$

One knows that from $-\frac \pi 2$ and $\frac \pi 2$, tan(t) is strictly increasing (from - infinity to + infinity). So it has only one solution if you want to solve tan(t)=...

Try for x=0.

(b) Find f(f -1(8)).
Huh ? Isn't $f(f^{-1}(x))=x$ ? (if f is a bijection ^-^)

I'm having a tough time finding the inverse.
And it will be very hard to find it