1.xy＋6－2x－3y2.x2(x－y)＋y2(y－x) 3.2x2－(a－2b)x－ab 4.a4－9a2b2 5.ab(x2－y2)＋xy(a2－b2) 6.(x＋y)(a－b－c)＋(x－y)(b＋c－a)7.a2－a－b2－b 8.(3a－b)2－4(3a－b)(a＋3b)＋4(a＋3b)2 9.(a＋3)2－6(a＋3) ...