f(x)＝x/(x^2-1)＝1/2×[1/(x-1)＋1/(x+1)]
函数y＝1/x在(－∞,0)∪(0,+∞)内单调减少,所以1/(x-1),1/(x+1)在(-1,1)内单调减少,所以函数f(x)在(-1,1)内单调减少