x² - 5x - 6
= x² + x - 6x - 6
= x(x + 1) - 6(x + 1)
= (x - 6) (x + 1)
x² + 3x - 40
= x² + 8x - 5x - 40
= x(x + 8) -5(x + 8)
= (x - 5) (x + 8)
x² + 3x - 4
= x² + 4x - x - 4
= x(x + 4) -1(x + 4)
= (x - 1) (x + 4)
