1/（x-1)-1/(x+1)首先，x不能为正负1。再将原式扩大（x-1）*(x+1)倍。（x-1)(x+1)*[1/（x-1)-1/(x+1)]=x+1-(x-1)=2再除以（x-1)(x+1)得2/（x^2-1)
x-1分之1-x+1分之1=(x+1)/(x-1)(x+1)-(x-1)/(x+1)(x-1)=2/(x-1)(x+1)=2/(x^2-1)
上下通分为得x²-1分之2
