2cos^2 3x+sin^2 3x = 1,5sin6x ^2 - квадрат

2cos²3x+sin²3x-3sin3xcos3x=0/cos²3x≠0
tg²3x-3tg3x+2=0
tg3x=a
a²-3a+2=0
a1+a2=3 U a1*a2=2
a1=1⇒tg3x=1⇒3x=π/4+πn⇒x=π/12+πn/3
a2=2⇒tg3x=2⇒3x=arctg2+πn⇒x=1/3arctg2+πn/3