3cos2x+7sinx cosx+sin^2x+3=0

3сos²x-3sin²x+7sinxcosx+sin²x+3cos²x+3sin²x=0/cos²x
tg²x+7tgx+6=0
tgx=a
a²+7a+6=0
a1+a2=-7 U a1*a2=6
a1=-6⇒tgx=-6⇒x=-arctg6+πn,n∈z
a2=-1⇒tgx=-1⇒x=-π/4+πk,k∈z