cos4a-2sin2acos2a*cos2a/sin2a= cos4a-2cos²2a=cos²2a-sin²2a-2cos²2a=-sin²2a-cos²2a=-(sin²2a+cos²2a)=-1 тождество верно
ctg 315= ctg(360-45)=-ctg45=-1
Y=2sin^2 2x
y'=2*2sin 2x *(sin2x)'=4sin 2x *cos 2x *(2x)'=8sin 2x cos 2x=4sin 4x
А) 5y(x-3)
б) 7ab^2 *(3a^2 -2b)