A/(X-1)+B/(X+2)=[A(X+2)+B(X-1)]/[(X-1)(X+2)]=[(A+B)X+(2A-B)]/[(X-1)(X+2)]=(2X-3)/[(X-1)(X+2)]A+B=2,2A-B=-3A=-1/3,B=7/3
(2x-3)/(x+1)(x+2)=A/(x+1)+B/(x+2)
=[A(x+2)+B(x+1)]/(x+1)(x+2)
=[(A+B)x+(2A+B)]/(x+1)(x+2)
∴{A+B=2 2A+B=-3
解得：A=-5 B=7
等下啊
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