#### Answer

$20=x$

#### Work Step by Step

The Pythagorean Theorem states that if $a$ and $b$ are the legs of a right triangle and $c$ is the hypotenuse, then $a^2+b^2=c^2$. We plug in the values for $a$, $b$, and $c$, using the legs and the hypotenuse of the right triangle shown, and then solve the equation using the properties of algebra and equality: $$12^2+16^2=x^2$$$$144+256=x^2$$$$400=x^2$$$$\sqrt {400}=\sqrt {x^2}$$$$20=x$$