Elementary Geometry for College Students (7th Edition)

$AC=13$
If $AB=5$ and $BC=12$, and $\angle B$ is a right angle, then $\triangle ABC$ is a right triangle with leg lengths of 5 and 12. Using The Pythagorean Theorem... $5^{2}+12^{2}=c^{2}$ $25+144=c^{2}$ $169=c^{2}$ $c=13$ $AC=13$