m/(x+1)(x-2)=x/x+1- x-2/x-2
方程两边的分母同时乘以(x+1)(x-2)得
m=x(x-2)-(x+1)(x-2)
m=(x-2)(x-x-1)
m=-(x-2)
m=-x+2
x=2-m
x>0 2-m>0
-m>-2
m