87. Решите уравнение: a) \( 3 + a = 5\frac{1}{7} \); б) \( x + 2\frac{1}{3} = 5\frac{1}{7} \)

Решение:

1. a) \( 3 + a = 5\frac{1}{7} \) \( a = 5\frac{1}{7} - 3 \) \( a = 2\frac{1}{7} \)
2. б) \( x + 2\frac{1}{3} = 5\frac{1}{7} \) \( x = 5\frac{1}{7} - 2\frac{1}{3} \) \( x = \frac{36}{7} - \frac{7}{3} \) \( x = \frac{36 \cdot 3}{7 \cdot 3} - \frac{7 \cdot 7}{3 \cdot 7} \) \( x = \frac{108}{21} - \frac{49}{21} \) \( x = \frac{59}{21} = 2\frac{17}{21} \)

Ответ: a) \(a = 2\frac{1}{7}\), б) \(x = 2\frac{17}{21}\).