Chapter 12.6, Problem 10WE

To determine

To find the indicated part of triangle ABC.

Answer to Problem 10WE

  $C={104.5}^{\circ }$

Explanation of Solution

Given information :

  

Here we shall use the cosine formula.

Cosine formula states that,

  $\cos A=\frac{b^2+c^2-a^2}{2bc}$

Now we have to find largest angle.

Largestangle is always opposite to the largest side.

Hence we find the angle opposite to largest side.

Hence we put the values given,

  $\begin{array}{l}\cos C=\frac{{30}^2+{20}^2-{40}^2}{2\left(30\right)\left(20\right)}\\ \cos C=\frac{-300}{1200}\\ C={\cos }^{-1}-0.25\\ C={104.5}^{\circ }\end{array}$