РОЗДІЛ 4. Квадратні рівняння » 788

788. Скориставшись теоремою Вієта, розв’яжіть квадратне рівняння: 1) x2 + 8x – 9 = 0. x1 + x2 = –8, x1 • x2 = –9; x1 = –9; x2 = –1. 2) x2 – 3x – 10 = 0; x1 + x2 = 3; x1 • x2 = –10; x1 = –2; x2 = 5. 3) x2 – 9x + 20 = 0; x1 + x2 = 9; x1 • x2 = 20; x1 = 4; x2 = 5. 4) x2 + 9x + 8 = 0; x1 + x2 = –9; x1 • x2 = 8; x1 = –1; x2 = –8. 5) x2 – 5x – 14 = 0. x1 + x2 = 5; x1 • x2 = –14. x1 = –2; x2 = 7. 6) x2 + 6x + 8 = 0. x1 + x2 = –6; x1 • x2 = 8. x1 = –2; x2 = –4. 7) x2 – x – 20 = 0. x1 + x2 = 1; x1 • x2 = –20. x1 = –4; x2 = 5. 8) x2 – 7x + 10 = 0. x1 + x2 = 7; x1 • x2 = 10. x1 = 2; x2 = 5.