Chapter 11 - Review Exercises - Page 525: 10

$α = 60^{\circ}$

$cos(α) = \frac{(14)^{2} + (16)^{2} - (15)^{2}}{2(14)(16)}$ $cos(α)= \frac{196+256-225}{448}$ $cos(α) = \frac{227}{448}$ $cos(α) = 0.50669....$ by GDC / calculator $α = 59.5559...^{\circ}$ $α = 60^{\circ}$