Chapter 7 - Applications of Trigonometric Functions - Section 7.3 The Law of Cosines - 7.3 Assess Your Understanding - Page 559: 15

$A \approx127.2^\circ$ $B \approx32.1^\circ$ $C\approx 20.7^\circ$

1. Use the Law of Cosines, we have $A=cos^{-1}(\frac{(6)^2+(4)^2-(9)^2}{2(6)(4)})\approx127.2^\circ$ 2. Use the Law of Sines, we have $\frac{sinB}{6}=\frac{sin127.2^\circ}{9}$ 3. We have $B=sin^{-1}(\frac{6sin127.2^\circ}{9})\approx32.1^\circ$ 4. We have $C\approx180-127.2-32.1=20.7^\circ$