## Elementary Geometry for College Students (7th Edition)

$c^{2}= a^{2} +b^{2}- 2\times a \times b \times 0= c^{2}= a^{2} +b^{2}$
If $\gamma = 90^{\circ}$, then $\cos \gamma =0$ Therefore, if we replace $\cos \gamma$ by 0 in the equation, we get $c^{2}= a^{2} +b^{2}- 2\times a \times b \times 0$ $c^{2}= a^{2} +b^{2}$ And that is the Pythagorean Theorem