通分=[A(x+2)+B(x-1)]/(x+2)(x-1)=[(A+B)x+(2A-B)]/(x-1)(x+2)=(3x-1)/(x-1)(x+2)所以(A+B)x+(2A-B)=3x-1A+B=32A-B=-1A=2/3B=7/3A/B=2/7