(x- x x+1 )÷(1+ 1 x2?1 )= x(x+1)?x x+1 ÷ x2 x2?1 = x2 x+1 × (x+1)(x?1) x2 =x-1;把x= 3 -1代入上式得:x-1= 3 -1-1= 3 ?2.