Bjr

x² + 2x - 15

discriminant = b² - 4ac = 2² - 4 * 1 * - 15 = 4 + 60 = 64

x1 = (- 2 + 8)/(2 * 1) = 6/2 = 3

x2 = (-2 - 8)/(2 * 1) = -10/2 = -5

donc x² + 2x - 15 = (x - 3)(x + 5)