122. Решите уравнения: a) x/12 - 5 = -x/18; б) 3 - x/15 = x/12; г) x/20 = -7 + x/25.

Решение:

1. \( \frac{x}{12} - 5 = -\frac{x}{18} \)

\( \frac{x}{12} + \frac{x}{18} = 5 \)
\( \frac{3x + 2x}{36} = 5 \)
\( 5x = 180 \)
\( x = 36 \)
2. \( 3 - \frac{x}{15} = \frac{x}{12} \)

\( 3 = \frac{x}{12} + \frac{x}{15} \)
\( 3 = \frac{5x + 4x}{60} \)
\( 3 = \frac{9x}{60} \)
\( 9x = 180 \)
\( x = 20 \)
3. \( \frac{x}{20} = -7 + \frac{x}{25} \)

\( \frac{x}{20} - \frac{x}{25} = -7 \)
\( \frac{5x - 4x}{100} = -7 \)
\( x = -700 \)

Ответ: a) \( x = 36 \); б) \( x = 20 \); г) \( x = -700 \).