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

using theorem 11.4.3 Law of cosine cos α = $\frac{5^{2} + 9^{2} - 7^{2}}{2(5)(9)}$ cos α =$\frac{25 + 81 - 49}{90}$ cos α =0.6333 α = $cos^{-1}$(0.6333) α = 50.7°