20. 4x² - 17x - 15 = 0

a = 4, b = -17, c = -15 D = (-17)² - 4 * 4 * (-15) = 289 + 240 = 529 x₁ = (17 + √529) / 2 * 4 = (17 + 23) / 8 = 40 / 8 = 5 x₂ = (17 - √529) / 2 * 4 = (17 - 23) / 8 = -6 / 8 = -3/4 Ответ: x₁ = 5, x₂ = -3/4