9,10

Solve the system of equations:

$x^{2}+4 \sin ^{2} y-4=0$,

$\cos x-2 \cos ^{2} y-1=0$.
$2 \cos ^{2} y=\cos x-1 \leq 0$, from which $\cos ^{2} y=0, \sin ^{2} y=1$. Now from the first equation we get $x=0$.

## Answer

$x=0, y=\pi / 2+k \pi$