A/(x-1)+B/(x+2) =[A(x+2)+B(x-1)]/(x-1)(x+2)=(2x-3)/(x-1)(x+2)所以A(x+2)+B(x-1)=2x-3(A+B)x+(2A-b)=2x-3所以A+B=22A-B=-3相加3A=-1A=-1/3,B=2-A=7/3
