x^2-4xy+3y^2=0
(x-y)(x-3y)=0
x=y或x=3y
当x=y时
(x-y)/(x+y)
=(y-y)/(y+y)
=0/2y
=0
当x=3y时
(x-y)/(x+y)
=(3y-y)/(3y+y)
=2y/4y
=1/2x^2-4xy+3y^2=0(x-y)(x-3y)=0这一步是怎么由上面算出来的？因式分解