Вопрос от пользователя: Флавия
1) 3 х-4=8
2) 12-2 Х=-10
3) 2 Х+3=10
4) 14 Х-7=28
5) (Х-3) (15-Х) = 0
6) (2 Х-20) (3+3 Х) = 0
7) (12-3 Х) (25-5 Х) = 0
Ответ: Денисыч
1) 3x — 4 = 8
3x = 12
x = 4
2) 12 — 2x = — 10
— 2x = — 22
x = 11
3) 2x + 3 = 10
2x = 7
x = 3,5
4) 14x — 7 = 28
14x = 35
x = 2,5
5) (x — 3) (15 — x) = 0
15x — x² — 45 + 3x = 0
— x² + 18x — 45 = 0
x² — 18x + 45 = 0
D = b² — 4ac = 324 — 4*45 = 324 — 180 = √144 = 12
x₁ = 18 + 12/2 = 15
x₂ = 18 — 12/2 = 3
6) (2x — 20) (3 + 3x) = 0
6x + 6x² — 60 — 60x = 0
6x² — 54x — 60 = 0
D = 2916 — 4*6 * ( — 60) = 2916 + 1440 = 4356
x₁ = 54 + 66 / 12 = 10
x₂ = 54 — 66/12 = — 1
7) (12 — 3x) (25 — 5x) = 0
300 — 60x — 75x + 15x² = 0
15x² — 135x + 300 = 0
D = 18225 — 4 * 15 * 300 = 18225 — 18000 = √225 = 15
x₁ = 135 + 15/30 = 5
x₂ = 135 — 15/30 = 4
