x^2+1/1-x=a化简-x-1+2/(1-x) = a(1-x) + 2/(1-x) = a + 2设t = 1 - x则 t + 2/t = a + 2左边是一个对勾函数所以 当 -2倍根2 < a + 2 < +2倍根2即 -2倍根2 - 2 < a < +2倍根2 - 2