What is the largest angle measure in a triangle with sides of lengths 3, 8, and 7?
The largest angle is opposite the longest side
Let A be that angle
Using the Law of Cosines
8^2 = 3^2 + 7^2 - 2 (3)(8) cos A
cos A = [ 8^2 - 3^2 - 7^2 ] / [ -2 * 3 * 8 ]
arccos [ ( 8^2 - 3^2 - 7^2 ) / ( -2 * 3 * 8 ) ] = A = 97.18°