Вправи: 830

830. Розв’яжіть рівняння:

1) x² – 4x – 5 = 0;

D = (–4)² – 4 • 1 • (–5) = 36; D = 6;

x₁ = 4+62 = 5; x₂ = 4-62 = –1.

2) 2x² + 7x – 4 = 0;

D = 7² – 4 • 2 • (–4) = 81; D = 9;

x₁ = -7+ 92 •2 = 24 = 0,5; x₂ = -7- 92 •2 = -164 = –4.

3) 3x² – 12x + 36 = 0;

D = (–12)² – 4 • 1 • 36 = 0;

x₁ = –-122 = 6.

4) x² – x – 56 = 0;

D = (–1)² – 4 • 1 • (–56) = 225; D = 15;

x₁ = 1+152 = 8; x₂ = 1-152 = –7.