因式分解分组分解

因式分解——分组分解法1.x2-4x-y2+42.4xy2-2xy+4x2-1\3.x2+x-y2-y4.7m2-3n+mn-21m5.x5y2-x3-3xy+36.13m4-13m3+m2-17.a2+6ab+9b2-16x2y28.ax2+ay2-2axy-ab29.x2+y2-x2y2-2xy10.1-x2-6xy-9y211.x2-6xy+9y2-4x+12y12.9a2+18a+9-b2-4b-413.a2-4ab+3b2+2bc-c214.x4+2x3+6x2+10x+515.(1-a2)(1-b2)-4ab16.x2-4-x2y+4xy-4y17.m2(m+n)2-n2(n-m)218.4m2n2-(m2+n2-x2)219.(m-2n)4-2m2-8n2+8mn+120.ab(x2+y2)+xy(a2+b2)