#### Answer

$\angle$1 + $\angle$2 = $90$
hence proved

#### Work Step by Step

Sum of angles of a triangle = $180^{\circ}$
$\angle$1 + $\angle$2 + $\angle$c = 180
given
$\angle$c = 90
$\angle$1 + $\angle$2 + 90 = 180
$\angle$1 + $\angle$2 = $90$
hence proved