1.=-(4x²-16xy+16y²)
=-(2x-4y)²
2.=9y-6y+²y²(a-b)(x-y)+(a-b)(x+y)
=9y-6y²+(y³x-y”+x+y)(a-b)
=3y(3-2y)+(y³x-y”+x+y)(a-b)
3.