Question

Suppose sinA = 12/13 with 90º≤A≤180º. Suppose also that sinB = -7/25 with -90º≤B≤0º. Find cos(A + B).

Answer 1

Firstly find cos(A) and then cos(B).

Then use:
\[\cos(A + B) = \cos(A)\cos(B) - \sin(A)\sin(B)\]

Answer 2

253/325 the correct answer