Повторюємо алгебру за 8 клас: 68

68. Розкладіть на множники квадратний тричлен:

1) x² – 5x – 6 = (x + 1)(x – 6);

x₁ + x₂ = 5; x₁ • x_{2 =} –6;

x₁ = –1; x₂ = 6.

2) 3x² – 4x + 1 = 3(x – 13)(x – 1) = (3x – 1)(x – 1);

D = (–4)² – 4 • 3 • 1 = 16 – 12 = 4.

x₁ = 4 -4 2 • 3 = 4 - 26 = 26 = 13;

x₂ = 4 + 42 • 3 = 4 + 26 = 66 = 1.

3) –2x^{2 +} 7x – 3 = –2(x – 12)(x – 3) = (–2x + 1)(x – 3) = (1 – 2x)(x – 3).

D = 7² – 4 • (–2) • (–3) = 49 – 24 = 25.

x₁ = -7 -252 • (-2) = -7 -5-4 = -12-4 = 3;

x₂ = -5 + 5-4 = -2-4 = 12.