Chapter 14 - Trigonometric Identities and Equations - 14-5 The Law of Cosines - Practice and Problem-Solving Exercises - Page 939: 8

$x \approx 27.9$

The Law of Cosines must be used in the form $e^{2}=d^{2}+f^{2}-2df\cos{E}$. $e^{2}=d^{2}+f^{2}-2df\cos{E}$ $x^{2}=35.2^{2}+31.7^{2}-2(35.2)(31.7)\cos{49°}$ $x^{2} \approx 779.8162$. $x \approx \sqrt {779.8162}$ $x \approx 27.9$