已知6x/x^2-9=A/x+3+B/x-3,求A-B的值

问题描述:

已知6x/x^2-9=A/x+3+B/x-3,求A-B的值

待定系数法,等号右边通分A(x-3)/(x^-9)+B(x+3)/(x^2-9)=(AX-3A+Bx+3B)/(x^2-9)=6x/(x^2-9)
(A+B)=6
3B-3A=0 ,A=B
A=B=3