1) b^3 - 8c^3 = (b-2c)(b^2+2bc+4c^2)
2) 49x^2y - y^3 = y(49x^2 - y^2) = y(7x-y)(7x+y)
3) -7a^2 + 14a - 7 = -7(a^2 - 2a + 1) = -7(a-1)^2
4) 5ab - 15b - 5a + 15 = 5(ab - 3b - a + 3) = 5(a(b-1)-3(b+1)) = 5(b-1)(a-3)
5) a^4 - 1 = (a^2 - 1)(a^2 + 1)
(3a + 1)(9a^2 - 3a + 1) = 27а^3 + 1 = 27/27 + 1 = 2