Use trigonometric identities to solve sin2 theta costheta

Use trigonometric identities to solve sin(2 theta) + cos(theta) = 0 exactly for 0 lessthanorequalto theta

sin(2theta) + cos theta=0

2 sin theta cos theta +cos theta=0

cos theta(2sin theta +1)=0

cos theta=0 , sin theta=-1/2

theta=pi/2,3pi/2 , theta=7pi/6,11pi/6

theta=pi/2 , 7pi/6,3pi/2,11pi/6