Question

If A and B are first-quadrant angles, and sin A = 0.8 and cos B = 1/3, find cos(A+B).

How would I go about solving this? Would I have to draw a triangle?

Answer 1

no, i think its asking u to use the eqn cos(A+B) = cosA*cosB - sinA*sinB

cuz' A and B are first-quadrant angles, u can use the eqn cos^2(A) + sin^2(A)=1 to find out the unknowns in the above eqn.

Answer 2

Thanks!

Answer 3

welcome :)