Solve the triangle with the given parts a 253 m b 127 m c

Solve the triangle with the given parts. a = 25.3 m, b = 12.7 m, c = 36.9 m What is the degree measure of angle A? (Round to the nearest tenth as needed.)

Solution

a = 25.3 b =12.7 ;c=36.9

apply cosine rule

cosA = (b^2 + c^2 - a^2)/2bc

=(12.7^2 + 36.9^2 - 25.3^2)/2*12.7*36.9

= 0.9419

A = 19.626 = 19.6 deg