Chapter 7 - Applications of Trigonometric Functions - Section 7.3 The Law of Cosines - 7.3 Assess Your Understanding - Page 559: 17

$c \approx2.57$ $A \approx 48.6^\circ$ $B\approx 91.4^\circ$

1. Use the Law of Cosines, we have $c=\sqrt {(3)^2+(4)^2-2(3)(4)cos40^\circ}\approx2.57$ 2. Use the Law of Sines, $\frac{sinA}{3}=\frac{sin40^\circ}{2.57}$, thus $A=sin^{-1}(\frac{3sin40^\circ}{2.57})\approx 48.6^\circ$ 3. We have $B\approx(180-40-48.6)=91.4^\circ$