(1) 6xy²–9x²y–y³ (2) (2a-b)²+8ab (
(1) 6xy²–9x²y–y³
(2) (2a-b)²+8ab
(3) (a-b)(x-y)-(b-a)(x+y)
(4) 4+12(x-y)+9(x-y)²