x+1分之A加x-1分之B=（x+1）（x-1)分之x-3[A(X-1)+B(X+1)]/(X+1)(X-1)=（x-3）/(X+1)(X-1)所以A(X-1)+B(X+1）=x-3(A+B)x+(A-B)=X-3所以A+B=1A-B=3解得A=2,B=-1
通分，然后对应项系数相等，A=2，B=-1
