Question 602898
cos(A + B) = [cos(A) * cos(B)] - [sin(A) * sin(B)]


you can use Pythagoras to find the missing functions
___ cos(A) = 40 / sqrt(40^2 + 9^2)
___ sin(A) = 9 / sqrt(40^2 + 9^2)


B is part of a 3-4-5 triangle , so sin(B) = -3/5



just figured out that 9-40-? is also a Pythagorean triple