а) x² + 5x - 36 = 0. D = 25 - 4(1)(-36) = 25 + 144 = 169. x = (-5 ± 13) / 2. x₁ = 4, x₂ = -9.
б) x³ + x = 0. x(x² + 1) = 0. x = 0.