X平方减1分之2X减3等于X减1分之A加上X分之B
应该是(2x-3)/(x^2-1)=A/(x-1)+B/(x+1)
=[(A+B)x+(A-B)]/(x^2-1)
可见A+B=2 A-B=-3
解得A=-1/2 B=5/2