Elementary Geometry for College Students (7th Edition) Clone

By using theorem 11.4.3 $c^{2}$ = $a^{2}$ + $b^{2}$ - 2ab cos γ $5^{2}$ = $3^{2}$ + $4^{2}$ - 2*3*4* cos γ 25 = 9 + 16 - 24cos γ 25 = 25 - 24cos γ 25 - 25 = - 24cos γ 0 = - 24cos γ cos γ = 0 γ = $cos^{-1}$(0) γ = 90°