Given the following side lengths in meters find the measure

Given the following side lengths (in meters), find the measure of angle A in radians to three decimal places. a = 29, b = 20, c = 15

Solution

a = 29

b = 20

c = 15

Using law of cosines

cos(A) = (b² + c² a²)/2bc = (20^2 + 15^2 - 29^2)/(2*20*15) = -0.36

A = arccos(-0.36)

A = 1.939 radians