Відповіді до вправ § 20 - § 26: 21.17

21.17 Розв’яжіть рівняння:

1) 12x² + x – 3 = 0; x² + 2x – 6 = 0;

D = 2² – 4 • 1 • (–6) = 28; D = 28 = 27;

x_1,2 = -2 ±272 = 2(-1±7)2 = –1 ± 7.

2) –x² + 2x + 11 = 0; x² – 2x – 11 = 0;

D = (–2)² – 4 • 1 • (–11) = 48; D = 48 = 43;

x_1,2 = 2 ±432 = 2(1±23)2 = 1 ± 3.

3) 0,2x² + 2x – 3 = 0; x² + 10x – 15 = 0;

D = 10² – 4 • 1 • (–15) = 160; D = 160 = 410;

x_1,2 = -10 ±4102 = 2(-5±210)2 = –5 ± 210.

4) 0,5 x² – 2,5x – 4 = 0; x² – 5x – 8 = 0;

D = (–5)² – 4 • 1 • (–8) = 57;

x_1,2 = 5 ±572.