Вариант 3: Найди значение х

Решение:

1. \( 5x + 7 = 2x + 19 \)
   \( 5x - 2x = 19 - 7 \)
   \( 3x = 12 \)
   \( x = \frac{12}{3} \)
   \( x = 4 \)
2. \( 6x - 3 = 3x + 9 \)
   \( 6x - 3x = 9 + 3 \)
   \( 3x = 12 \)
   \( x = \frac{12}{3} \)
   \( x = 4 \)
3. \( 7x + 5 = x - 1 \)
   \( 7x - x = -1 - 5 \)
   \( 6x = -6 \)
   \( x = \frac{-6}{6} \)
   \( x = -1 \)
4. \( 4x + 8 = 2x - 2 \)
   \( 4x - 2x = -2 - 8 \)
   \( 2x = -10 \)
   \( x = \frac{-10}{2} \)
   \( x = -5 \)
5. \( 8x - 1 = 5x + 8 \)
   \( 8x - 5x = 8 + 1 \)
   \( 3x = 9 \)
   \( x = \frac{9}{3} \)
   \( x = 3 \)
6. \( 9x + 4 = 6x - 5 \)
   \( 9x - 6x = -5 - 4 \)
   \( 3x = -9 \)
   \( x = \frac{-9}{3} \)
   \( x = -3 \)
7. \( 3x + 6 = x - 2 \)
   \( 3x - x = -2 - 6 \)
   \( 2x = -8 \)
   \( x = \frac{-8}{2} \)
   \( x = -4 \)
8. \( 2x - 7 = 5x - 1 \)
   \( -7 + 1 = 5x - 2x \)
   \( -6 = 3x \)
   \( x = \frac{-6}{3} \)
   \( x = -2 \)
9. \( 6x + 9 = 2x - 7 \)
   \( 6x - 2x = -7 - 9 \)
   \( 4x = -16 \)
   \( x = \frac{-16}{4} \)
   \( x = -4 \)
10. \( 7x - 8 = 3x + 4 \)
    \( 7x - 3x = 4 + 8 \)
    \( 4x = 12 \)
    \( x = \frac{12}{4} \)
    \( x = 3 \)
11. \( 5x + 10 = 4x - 6 \)
    \( 5x - 4x = -6 - 10 \)
    \( x = -16 \)
12. \( 8x + 12 = 6x - 4 \)
    \( 8x - 6x = -4 - 12 \)
    \( 2x = -16 \)
    \( x = \frac{-16}{2} \)
    \( x = -8 \)

Ответ: 1. 4; 2. 4; 3. -1; 4. -5; 5. 3; 6. -3; 7. -4; 8. -2; 9. -4; 10. 3; 11. -16; 12. -8.