A triangular parcel of ground has sides of length 745 feet, 630 feet, and 580 feet. Find the measure of the largest angle. (Round your answer to one decimal place.)

Question

= _______°

Answer 1

largest angle is opposite the largest side

the angle remains the same if you reduce the sides by a common factor 5

149 - 126 - 116

use the law of cosines

149^2 = 126^2 + 116^2 -2(126)(116)cosA

cosA = -(149^2-126^-116^2)/2(126)(116)

if you do this right, cosA will be between -1 and +1. cosines are never larger than 1 or less than -1

cosA =0.2439

then use an inverse trig function on a scientific calculator to solve for A

A = 75.88 degrees = 75.9 rounded to one decimal place

(no guarantee of accurate arithmetic calculations, but it looks about right)