3
2sinxcosx+2cosx+2sinxcosx=0,sinx≠-1
2cosx(2sinx+1)=0
cosx=0⇒x=π/2+πn,n∈z
sinx=-1/2⇒x=(-1)^(n+1)*π/6+πk,k∈z
4
sin²x/2+cos²x/2-cos²x/2+sin²x/2-2sinx/2cosx/2=0,cosx≠0
2sin²x/2-2sinx/2cosx/2=0
2sinx/2(sinx/2-cosx/2)=0
sinx/2=0⇒x/2=πn,n∈z⇒x=2πn,n∈z
sinx/2-cosx/2=0/cosx/2
tgx/2-1=0⇒tgx/2=1⇒x/2=π/4+πk,k∈z⇒x=π/2+2πk,k∈z