А) х² - 3х - 54 = 0
D = (-3)² - 4 * 1 * (-54) = 225
3 - √225 3 - 15
х₁ = -------------- = --------- = - 6
2 * 1 2
3 + √225 3 + 15
х₂ = --------------- = ------------- = 9
2 * 1 2
2) у² + 15у + 56 = 0
D = 15² - 4 * 1 * 56 = 1
- 15 - √1
х₁ = ------------- = - 8
2 * 1
- 15 + √1
х₂ = --------------- = - 7
2 * 1
3) а² - 19а + 60 = 0
D = (-19)² - 4 * 1 * 60 = 121
- (-19) - √121 19 - 11
х₁ = --------------------- = ---------- = 4
2 * 1 2
19 + √121
х₂ = --------------- = 15
2 * 1
3) - b² - 3b + 70 = 0
D = (- 3)² - 4 * (- 1) * 70 = 289
3 - √289 3 - 17
х₁ = -------------- = --------- = 7
2 * (-1) - 2
3 + 17
х₂ = ------------- = - 10
- 2