x²-4x-21 = x²+3x-7x-21 = x(x+3)-7(x+3) = (x+3)(x-7)
Răspuns:
x² - 4x - 21 =
= x² + 3x - 7x - 21
= x(x + 3) - 7(x + 3)
= (x + 3)(x - 7)