Повторюємо алгебру за 8 клас: 67

67. Розкладіть на множники квадратний тричлен:

1) x² – 7x + 6 = (x – 1)(x – 6);

x₁ + x₂ = 7; x₁ • x₂ = 6;

x₁ = 1; x₂ = 6.

2) 2x² + 5x + 2 = 2(x + 12)(x + 2) = (2x + 1)(x + 2).

D = 5² – 4 • 2 • 2 = 25 – 16 = 9.

x₁ = -5 - 92 • 2 = -5 - 34 = -84 = –2;

x₂ = -5 + 34 = -24 = –12.

3) –3x² – 5x + 2 = –3(x – 13)(x + 2) = (–3x + 1)(x + 2);

D = (–5)² – 4 • (–3) • 2 = 25 + 24 = 49;

x₁ = 5 - 492 • (-3) = 5 - 7-6 = -2-6 = 13;

x₂ = 5 + 7-6 = 12-6 = –2.