How do I find sin2x+cosx=0, using a double angle or half angle? I got 11pi/6, 3pi/2, 7pi/6, pi/2.

Question

anonymous · Answer

But I got the answers wrong so idk what to do.

campbell_st · Answer

well use sin(2x) = 2sin(x)cos(x)

so the equation becomes

2sin(x)cos(x) + cos(x) = 0

now factor

cos(x)(2sin(x) + 1) = 0

hope it helps you get a solution.

anonymous · Answer

Thats exactly what I did but my answers came out wrong @campbell_st

campbell_st · Answer

so you have 

cos(x) = 0   and sin(x) = -1/2

anonymous · Answer

yup @campbell_st

campbell_st · Answer

I just graphed it and got those solutions.... so I really can't  help. It could be a mistake in the answers provided or a typo in the question.

anonymous · Answer

Its ok thnx anyway @campbell_st