soluzione Calcolare ( x x + y + y2 x2 - y2 ) : ( x2 x2 - y2 + y3 x3 - xy2 )   =   ( x x + y + y2 (x - y)(x + y) ) : ( x2 (x - y)(x + y) + y3 x(x - y)(x + y) )   =     =   x(x - y) + y2 (x - y)(x + y) : x3 + y3 x(x - y)(x + y)   =     =   x2 - xy + y2 (x - y)(x + y) : x3 + y3 x(x - y)(x + y)   =     =   x2 - xy + y2 (x - y)(x + y) · x(x - y)(x + y) x3 + y3   =     =   x2 - xy + y2 (x - y)(x + y) · x(x - y)(x + y) (x + y)(x2 - xy + y2)   =     =   x x + y