1. ## Cosine...

If $cos^{-1}(x)+cos^{-1}(y)=\frac{\pi}{2}$,
show that $x^2+y^2=1$

2. Originally Posted by fizz
If $cos^{-1}(x)+cos^{-1}(y)=\frac{\pi}{2}$,
show that $x^2+y^2=1$

Let
$cos^{-1}(x) = m$
$cos^{-1}(y) = n$

So we have:
$m + n = \frac{\pi}{2}$

Also, from above, we have:

$x= \cos m$
$y= \cos n$

Can you finish the rest?

Good luck!