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

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