121. Решите уравнения: a) x/4 = 3/2 + x; б) x/21 = 8/7 - x/7; г) x/30 = 4 - x/6.

Решение:

• а) x/4 = 3/2 + x
1. x/4 - x = 3/2
2. x/4 - 4x/4 = 3/2
3. -3x/4 = 3/2
4. -3x = (3/2) * 4
5. -3x = 6
6. x = 6 / -3
7. x = -2
• б) x/21 = 8/7 - x/7
1. x/21 + x/7 = 8/7
2. x/21 + 3x/21 = 8/7
3. 4x/21 = 8/7
4. 4x = (8/7) * 21
5. 4x = 8 * 3
6. 4x = 24
7. x = 24 / 4
8. x = 6
• г) x/30 = 4 - x/6
1. x/30 + x/6 = 4
2. x/30 + 5x/30 = 4
3. 6x/30 = 4
4. x/5 = 4
5. x = 4 * 5
6. x = 20

Ответ: а) -2; б) 6; г) 20.