(a)2 * (b)2 = (a * b)2
Wir lassen also erstmal die Quadrate weg
(1 + a) * (a - 1 + 1/(a + 1))
= a - 1 + 1/(a + 1) + a2 - a + a/(a + 1)
= - 1 + 1/(a + 1) + a2 + a/(a + 1)
= - (a + 1)/(a + 1) + 1/(a + 1) + a2 + a/(a + 1)
= a2
Das kann men jetzt leicht quadrieren
(a2)2 = a4