已知分式x平方+1分之x（x-3）的值为0,
x(x-3)=0
x=0 或x=3
则x平方-1分之2x除以1-x分之3x值
=2x/(x^2-1) *(1-x)/3x
=2x/(x-1)(x+1) *[-(x-1)/3x]
=-2/3(x+1)
(1)x=0
上式=-2/3(x+1)=-2/3(0+1)=-2/3
(2)x=3
上式=-2/3(x+1)=-2/3(3+1)=-1/6