x2-xy-6y2+3x-9y=0可以转化为(x-3y)(x+2y)+3(x-3y)=0,知道了,但是转化的方法是什么?有方法吗?

解方程组 ｛3x2-y2=8 {4x2+12xy+9y2=1 {x2+2xy+y2-4=0 x2+xy+y2=4 4x2-9y2=0 x2-2xy+y2-1=0还有{x2+y2=4xy-y2+4=0x2-----x的平方 y2------y的平方 还有{2x-3y=12x2-3xy+y2-4x+3y-3=0 若X2+Y2-2X-6Y+10=0 ,求（x2-y2)/xy的值 计算(x+y/x-y + 4xy/y2-x2)(x2-9y2)/（x2+2xy-3y2） x2+2xy+y2-9=0 (x-y)2-3(x-y)+2=0 x2-2xy-3y2=0,其中x,y均不为零,求（y-x）/x2-xy/2x-y-y2/xy-x 已知X2-2x+y2+6y+10=0,求（x2-2xy）/(xy+y2)的值 若2分之x=3分之y,求x2-6xy-7y2分之x2-2xy-3y2 若x/y=2,求x2-2xy-3y2/x2-6xy-7y2的值 已知实数x,y满足x2+xy+y2=3,则x2-xy+y2的最小值 (x+√(x2+2011))(y+(√y2+2011))=2011,x2-3xy-4y2-6x-6y+58 x2-2xy+y2=4 x2+y2-x-y=6 解不等式x2-2xy+y2=4 x2+y2-x-y=6 解不等式 已知X2+Y2+8X+6Y+25=0 求代数式X2++XY+4Y2分之X2-4Y2 减X+2Y分之X的值 X2+Y2+8X+6Y+25=0 求代数式(x2-4y2/x2+4xy+4y2)-x/x+2y 已知x2+4y2+x2y2+1=6xy,则(x4-y4)/(2x2+xy-y2)*(2x-y)/(xy-y2)/(x2+y2/y)2= x3+6xy+y3 =x3+y3+6xy =(x+y)(x2-xy+y2)+6xy 为什么x3+y3+6xy可以化成(x+y)(x2-xy+y2)+6xy请为我解释一下恕我浅薄， 已知x2-3xy-4y2的绝对值+2倍根号x2+4xy+4y2-1=0 求3x+6y的值 已知：x2-y2=16,x+y=2,求：3x-3y/y2-x2+x2-2xy+y2/x2-y2-x2-x-6/x+2除以(x+y) x2-4y2-3xy+y+x