Вправи: 838

838. Розв’яжіть рівняння:

1) x2- 3x4 = 2x+53; 3(x² – 3х) = 4(2х + 5); 3x² – 9x = 8х + 20;

3x² – 9x – 8х – 20 = 0; 3x² – 17x – 20 = 0;

D = (–17)² – 4 • 3 • (–20) = 529; D = 23;

х₁ = 17+232 • 3 = 406 = 623; х₂ = 17-236 = –1.

2) x+12 + x2-15 = 1 |х10;

5(x + 1) + 2(x² – 1) = 10; 5х + 5 + 2x² – 2 – 10 = 0;

2x² + 5x – 7 = 0;

D = 5² – 4 • 2 • (–7) = 81; D = 9;

х₁ = -5+92 • 2 = 44 = 1; х₂ = -5-94 = -144 = –3,5.