Answer
$AC=13$
Work Step by Step
Given rectangle $ABCD$ with side lengths of $AD=12$ and $DC=5$, we can use the Pythagorean Theorem to find the length of the diagonal.
$12^{2}+5^{2}=c^{2}$
Simplify...
$144+24=c^{2}$
Combine like terms...
$169=c^{2}$
Square root both sides...
$c=13$ or diagonal $AC=13$
