y=4sin2xcos2x-4cos²2x
=2*(2sin2xcos2x)-4(1+cos4x)/2
=2sin4x-2cos4x-2
=2√2(√2/2*sin4x-√2/2*cos4x)-2
=2√2(sin4xcosπ/4-cos4xsinπ/4)-2
=2√2sin(4x-π/4)-2
-1