题目先化简,再求值:(1−xx−1)÷xx2−1(1-\frac{x}{x-1})÷\frac{x}{{{x^2}-1}}(1−x−1x)÷x2−1x,其中xxx满足x2+3x−4=0x^{2}+3x-4=0x2+3x−4=0.知识点：分式的化简求值章节：数与式 / 分式
