7/(x²+x) + 1/(x²-x) = 6/(x²-1)
方程两边同时乘以x(x+1)(x-1)：7(x-1) + (x+1) = 6x
解得：x = 3
x = 3时：x(x+1)(x-1) ≠ 0
x = 3是原方程的根