Вправи: 832

832. Розв’яжіть рівняння:

1) 10x² = 0,4 – 3x; 10x² + 3x – 0,4 = 0;

D = 3² – 4 • 10 • (–0,4) = 25; D = 5;

x₁ = -3+52 •10 = 220 = 0,1; x₂ = -3-520 = –0,4.

2) x² + 7 = –8x; x² + 8x + 7 = 0;

D = 8² – 4 • 1 • 7 = 36; D = 6;

x₁ = -8+62 = –1; x₂ = -8-62 = –7.

3) 7x = x² + 12; x² – 7x + 12 = 0;

D = (–7)² – 4 • 1 • 12 – 1; D = 14;

x₁ = 7+12 = 4; x₂ = 7-12 = 3.

4) 4y = 4y² + 1; 4y² – 4y + 1 = 0;

D = (–4)² – 4 • 4 • 1 = 0;

y = –-42 • 4 = 12.