(x + 2)(x + 1) – (x – 3)(x + 5) = 0
⇔ x2 + x + 2x + 2 – (x2 + 5x – 3x – 15) = 0
⇔ x2 + 3x + 2 - x2 - 2x + 15 = 0
⇔ x + 17 = 0
⇔ x = -17.
