2x^3 - 5x^2 - 6x + 15 = x^2(2x - 5) - 3(2x - 5) = (x^2 - 3)(2x - 5)
9a^2 - 4b^2 = (3a + 2b)(3a - 2b)
3a^3 - 48a^2c = 3a^2(a - 16c)
81c^4 + 3b^3 = 3(b^3 + 27c^4) = 3(b + 3c)(b^2 - 3bc + 9c^2)
2x^3 - 5x^2 - 6x + 15 = x^2(2x - 5) - 3(2x - 5) = (x^2 - 3)(2x - 5)
9a^2 - 4b^2 = (3a + 2b)(3a - 2b)
3a^3 - 48a^2c = 3a^2(a - 16c)
81c^4 + 3b^3 = 3(b^3 + 27c^4) = 3(b + 3c)(b^2 - 3bc + 9c^2)