Question

Express cos P as a fraction in simplest terms. The letters are P, O, and N while the numbers are 15, 36, 39.

Answer 1

Label the triangle so the side opposite angle P is 15 and the two sides adjacent to P are 36 and 39. By the Law of Cosines,

cos P = (36^2 + 39^2 − 15^2) / (2·36·39)
= 2592 / 2808
= 12/13.