#### Answer

$13$

#### Work Step by Step

According to the Pythagoras Theorem, if $a$ and $b$ are the lengths of the legs of a right triangle, and $c$ is the length of the
hypotenuse, then $a^{2}+b^{2}=c^{2}$.
Since $a=5$ and $b=12$, we substitute these values in the formula and solve:
$c^{2}=a^{2}+b^{2}=5^{2}+12^{2}=25+144=169$
Therefore, $c=\sqrt (169)=13$
Since $c$ represents a length, we assume that $c$ is positive and is equal to $13$.