Answer
$x = 9$
Work Step by Step
In a $45^{\circ}-45^{\circ}-90^{\circ}$ triangle, the hypotenuse is $\sqrt 2$ times each leg. Let's write an equation to solve for $x$, the length of a leg:
$9\sqrt 2 = \sqrt 2(x)$
Divide each side by $\sqrt 2$ to solve for $x$:
$x = 9$
