Given that Alpha and Beta are in quadrant 2 and sinA=4/5 and cosB= -15/17 Find: CosA
Sin^2(A) + Cos^2(A)=1
4/5^2 + Cos^2(A)=1
Cos^2(A)=1 - .64=.36 take the sqrt of both sides,
Cos(A)=.6=3/5