Chapter 7 - Applications of Trigonometric Functions - Section 7.3 The Law of Cosines - 7.3 Assess Your Understanding - Page 559: 22

$a \approx4.58$ $B \approx 49.1^\circ$ $C\approx 10.9^\circ$

1. Use the Law of Cosines, we have $a=\sqrt {(4)^2+(1)^2-2(4)(1)cos120^\circ}\approx4.58$ 2. Use the Law of Sines, $\frac{sinB}{4}=\frac{sin120^\circ}{4.58}$, thus $B=sin^{-1}(\frac{4sin120^\circ}{4.58})\approx 49.1^\circ$ 3. We have $C\approx(180-120-49.1)=10.9^\circ$