## Elementary Geometry for College Students (5th Edition)

$\overline{DE}=12$
Let $b = \overline{DE}$ $13^{2} = 5^{2}+ b^{2}$ Isolate $b$ $13^{2}-5^{2}=b^{2}$ $169-25=b^{2}$ $144=b^{2}$ Square root each side $12=b$