Chapter 12.6, Problem 1OE

To determine

To use the law of cosines to give an equation involving the side or angle labeled $x$

Answer to Problem 1OE

  $\cos {42}^{\circ }=\frac{7^2+4^2-x^2}{2\left(7\right)\left(28\right)}$

Explanation of Solution

Given information :

  

Cosine formula states that,

  $\cos A=\frac{b^2+c^2-a^2}{2bc}$

Hence we put the values given,

  $\cos {42}^{\circ }=\frac{7^2+4^2-x^2}{2\left(7\right)\left(28\right)}$

Hence this is the required equation.