РОЗДІЛ 4. Квадратні рівняння » 787 (9-15)

9) x2 + 5x + 4 = 0; x1 + x2 = –5; x1 • x2 = 4; x1 = –1; x2 = –4. 10) x2 + 6x + 5 = 0; x1 + x2 = –6; x1 • x2 = 5; x1 = –1; x2 = –5. 11) x2 + x – 2 = 0. x1 + x2 = –1; x1 • x2 = –2. x1 = –2; x2 = 1. 12) x2 + 25x + 100 = 0; x1 + x2 = –25; x1 • x2 = 100; x1 = –5; x2 = –20. 13) x2 – 9x – 10 = 0. x1 + x2 = 9; x1 • x2 = –10. x1 = –1; x1 = 10. 14) x2 + 8x + 7 = 0. x1 + x2 = –8; x1 • x2 = 7. x1 = –1; x2 = –7. 15) x2 – 3x + 2 = 0; x1 + x2 = 3; x1 • x2 = 2. x1 = 1; x2 = 2.