## Elementary Geometry for College Students (6th Edition)

$AD=13$
In $\triangle ABC$ $AC^{2}=AB^{2}+BC^{2}$ $AC^{2}=4^{2}+3^{2}$ so AC = 5 In $\triangle ACD$ $AD^{2}=AC^{2}+DC^{2}$ $AD^{2}=5^{2}+12^{2}$ $AD^{2}=25+144$ $AD^{2}=169$ $AD=13$