Answer
$a*\sqrt 2$; You can always find the length of the hypotenuse of an isosceles right triangle by multiplying the length of the leg of the triangle by $\sqrt 2$.
Work Step by Step
The $a$ value can be inputted as both the $a$ and $b$ in the Pythagorean theorem formula because the sides are the same length. Take the square root of both sides and simplify for $c$.
$a^2+a^2=c^2$
$2a^2=c^2$
$\sqrt {2*a^2}=c$
$a*\sqrt 2=c$
