642. Решите уравнение: a) (x - 8) \cdot \frac{2}{5} = 2; б) \(2\frac{1}{3}x - 2\frac{2}{3} = 2\frac{1}{3}\)

a)

$$(x - 8) \cdot \frac{2}{5} = 2$$ $$x - 8 = 2 : \frac{2}{5}$$ $$x - 8 = 2 \cdot \frac{5}{2}$$ $$x - 8 = 5$$ $$x = 5 + 8$$ $$x = 13$$

б)

$$2\frac{1}{3}x - 2\frac{2}{3} = 2\frac{1}{3}$$ $$\frac{7}{3}x - \frac{8}{3} = \frac{7}{3}$$ $$\frac{7}{3}x = \frac{7}{3} + \frac{8}{3}$$ $$\frac{7}{3}x = \frac{15}{3}$$ $$x = \frac{15}{3} : \frac{7}{3}$$ $$x = \frac{15}{3} \cdot \frac{3}{7}$$ $$x = \frac{15}{7}$$ $$x = 2\frac{1}{7}$$

Ответ: a) 13; б) \(2\frac{1}{7}\)