Question

If the angle is in the 2nd quadrant, which is the correct angle? cos (pi/2+pi/3) or cos (pi-pi/3) ?

Answer 1

cos(pi/2+pi/3)= cos(5*pi/6)=cos(150)

cos(pi - pi/3)= cos(2*pi/3)= cos(120)
both angles lie on 2nd quadrant