need help, quickly!!!!

Question

In triangle ABC, what is the measure of C if a = 20, b = 15, and c = 19?

A.26.1°

B.42.33°

C.58.87°

D.63.9°

E.116.1°

Answer 1

Use Law of Cosines to solve for angle C's measure as follows:

cosC = (c² - a² - b²) / (-2ab)

Calculate the right-hand side of this equation, then take the cos^-1 of the decimal you get.