kalbim

Verified answer

X^2 - 2x - 15 = (x^2 - 2x + 1) - 16 = (x - 1)^2 - 4^2 = (x - 1 - 4)(x - 1+ 4) = (x - 5)(x + 3)
или через дискриминант:
x^2 - 2x - 15 = 0, D = 4 + 4*15 = 64
x1 = 5, x2 = -3