1)2sin²3x-√3sin3x=0
sin3x(2sin3x-√3)=0
sin3x=0⇒3x=πn⇒x=πn/3
sin3x=√3/2⇒3x=(-1)^n*π/3+πn⇒x=(-1)^n*π/9+πn/3
2)cos(3π/2+x)-5cosx=0
sinx-5cosx=0/cosx≠0
tgx-5=0
tgx=5
x=arctg5+πn
3)cos²x-7sin²x-6sinxcosx=0/cos²x≠0
7tg²x+6tgx-1=0
tgx=a
7a²+6a-1=0
D=36+28=64
a1=(-6-8)/14=-1⇒tgx=-1⇒x=-π/4+πn
a2=(-6+8)/14=1/7⇒tgx=1/7⇒x=arctg1/7+πn