Answer
$15$ cm
Work Step by Step
The Pythagorean Theorem is generally written as:
$a^2+b^2=c^2$,
in which $a$ and $b$ are the lengths of legs, and $c$ is the hypotenuse length in a right triangle.
This problem gives us the length of both legs, which are $9$ cm and $12$ cm, so we can replace $a$ and $b$ with these values and solve for $c$.
$c^2=a^2+b^2$
$c^2=9^2+12^2=81+144=225$
$c=\sqrt {225}=15$ cm
Note: $c^2=225$ could yield both $c=15$ and $c=-15$ as solutions in standard equations. However, because lengths cannot be negative, we only consider positive solutions in the Pythagorean Theorem.
