Question

A triangular plaque has side lengths 8 inches, 13 inches, and 15 inches. Find the measure of the largest angle.

Answer 1

Set your calculator to Degree mode.

15^2 = 8^2 + 13^2 - 2(8)(13)(cos x)

225 = 233 - 208(cos x)

8 = 208(cos x)

cos x = 1/26

`x = {cos}^( - 1) (1)/(26) = 87.8 \: degrees`

The measure of the largest angle is about 87.8°.