Вправи для повторення розділу 3 » 35

Розкладіть на множники квадратний тричлен: 1) x2 + Зх – 4. D = З2 – 4 • (–4) = 25; x1 = (-3+5)/2 = 1; x2 = (-3-5)/2 = –4. x2 + Зх – 4 = (х – 1)(х + 4). 2) 2x2 – 7x – 4. D = (–7)2 – 4 • 2 • (–4) = 81; x1 = (7+9)/4 = 4; x2 = (7-9)/4 = –1/2. 2x2 – 7x – 4 = 2(x – 4)(x + 1/2) = (x – 4)(2x + 1). 3) –x2 + 3x + 18. D = 9 + 4 • 18 = 81; x1 = (-3+9)/(-2) = 6/(-2) = –3; x2 = (-3-9)/(-2) = 6; –x2 + 3x + 18 = –(x + 3)(x – 6) = (x + 3)(6 – x). 4) –4x2 + 9x – 2. D = 92 – 4 • (–4) • (–2) = 49; x1 = (-9+7)/(-8) = 1/4; x2 = (-9-7)/(-8) = 2;