4(2x-y²-9(x+3y)²
=[2(2x-y)]²-[3(x+3y)]²
=(4x-2y)²-(3x+9y)²
=[(4x-2y)+(3x+9y)][(4x-2y)-(3x+9y)]
=(7x+7y)(x-11y)
=7(x+y)(x-11y)