a³ - 7a + 6 = (a³ - a) - (6a - 6) = a(a² - 1) - 6(a - 1) = a(a - 1)(a + 1) - 6(a - 1) =
= (a - 1)(a² + a - 6) = (a - 1)(a + 3)(a - 2)
a³ - 7a + 6 = (a³ - a) - (6a - 6) = a(a² - 1) - 6(a - 1) = a(a - 1)(a + 1) - 6(a - 1) =
= (a - 1)(a² + a - 6) = (a - 1)(a + 3)(a - 2)