1/(x2-2x-3) +2/(x2-x-6) +3/(x2+3x+2)=0
1/(x-3)(x+1)+2/(x-3)(x+2)+3/(x+1)(x+2)=0
两边同乘以(x+1)(x+2)(x-3)得：
(x+2)+2(x+1)+3(x-3)=0
x+2+2x+2+3x-9=0
6x=5
x=5/6