x^3 - 19x - 30
= (x^3 - 5x^2) + (5x^2 - 25x) + (6x - 30)
= x^2(x - 5) + 5x(x - 5) + 6(x - 5)
= (x^2 + 5x + 6)(x - 5)
= (x^2 + 2x + 3x + 6)(x - 5)
= (x(x + 2) + 3(x + 2))(x - 5)
= (x + 2)(x + 3)(x - 5)
x^3 - 7x - 6
= (x^3 - 3x^2) + (3x^2 - 9x) + (2x - 6)
= x^2(x - 3) + 3x(x - 3) + 2(x - 3)
= (x^2 + 3x + 2)(x - 3)
= (x^2 + 2x + x + 2)(x - 3)
= (x(x + 2) + (x + 2))(x - 3)
= (x + 1)(x + 2)(x - 3)