Presupun ca nu aveau bara deasupra
ab - ac = bc - c²
a( b - c) = c( b - c) /reducem b - c
a = c
b = c + 1, cum a = c => b = a + 1
2b - a - c = 2(a + 1) - a - a = 2a + 2 - a - a = 2 + a - a = 2 + 0 = 2
(a² - b²)(b² - c²)(c² - a²) = (a² - b²)(b² - c²) x 0 = 0