soluzione Calcolare x2 - 1 x2 + 1  ·  ( x x + 1   +   x x - 1 - 1)   =     =   x2 - 1 x2 + 1  ·  x(x - 1) + x(x + 1) - (x2 - 1) (x - 1)(x + 1)   =     =   x2 - 1 x2 + 1  ·  x2 - x + x2 + x - x2 + 1 (x - 1)(x + 1)   =     =   x2 - 1 x2 + 1  ·  x2 + 1 (x - 1)(x + 1)   =     =   (x - 1)(x + 1) x2 + 1  ·  x2 + 1 (x - 1)(x + 1)   =     = 1