Question

In triangle LMN, LM = 6, MN = 9, and LN = 7. Find m∠M to the nearest tenth of a degree.

Answer 1

7^2 = 6^2 + 9^2 - 2(6)(9)cos(m)
-68 = 2(6)(9)cos(m)
cos(m) = -0.6296
m = arcos ( -0.6296)
m = 129.0 degrees