25x^2 - 40x + 16 = 25x^2 - 20x - 20x + 16 = 5x(5x - 4) - 4(5x - 4) = (5x - 4)(5x - 4)
2x^2 + x + 4 cannot be factored.
6x^2 - 2x - 20 = 6x^2 - 12x + 10x - 20 = 6x(x - 2) + 10(x - 2) = (6x + 10)(x - 2)
x^2 - 2x - 4 cannot be factored using integral coefficients and integral constants.
