Question

化简 x x-1 - 1 x+1 的结果是（　　） A．1 B．x 2 +1 C．x 2 -1 D． x

化简 x x-1 - 1 x+1 的结果是（　　） A．1 B．x 2 +1 C．x 2 -1 D． x 2 +1 x 2 -1

Answer 1

原式= x(x+1) (x-1)(x+1) - x-1 (x+1)(x-1) = x 2 +x-x+1 x 2 -1 = x 2 +1 x 2 -1 ． 故选：D．