9. Решите уравнение: 1) -4x = 28; 2) 0,7x = -4,2; 3) -1,4x = -5,6; 4) 3/4 x = -2/9; 5) 4/7 x = 1; 6) 3x = 7; 7) 3/4 x = -12; 8) -2 1/3 x = 7/15; 9) 18x = 9.

Решение:

1. \( -4x = 28 \)
   \( x = \frac{28}{-4} \)
   \( x = -7 \)
2. \( 0,7x = -4,2 \)
   \( x = \frac{-4,2}{0,7} \)
   \( x = -6 \)
3. \( -1,4x = -5,6 \)
   \( x = \frac{-5,6}{-1,4} \)
   \( x = 4 \)
4. \( \frac{3}{4} x = -\frac{2}{9} \)
   \( x = -\frac{2}{9} \cdot \frac{4}{3} \)
   \( x = -\frac{8}{27} \)
5. \( \frac{4}{7} x = 1 \)
   \( x = 1 \cdot \frac{7}{4} \)
   \( x = \frac{7}{4} \)
   \( x = 1\frac{3}{4} \)
6. \( 3x = 7 \)
   \( x = \frac{7}{3} \)
   \( x = 2\frac{1}{3} \)
7. \( \frac{3}{4} x = -12 \)
   \( x = -12 \cdot \frac{4}{3} \)
   \( x = -4 \cdot 4 \)
   \( x = -16 \)
8. \( -2\frac{1}{3} x = \frac{7}{15} \)
   \( -\frac{7}{3} x = \frac{7}{15} \)
   \( x = \frac{7}{15} \cdot \left(-\frac{3}{7}\right) \)
   \( x = -\frac{1}{5} \)
9. \( 18x = 9 \)
   \( x = \frac{9}{18} \)
   \( x = \frac{1}{2} \)

Ответ: 1) x = -7; 2) x = -6; 3) x = 4; 4) x = -8/27; 5) x = 7/4; 6) x = 7/3; 7) x = -16; 8) x = -1/5; 9) x = 1/2.