Решите уравнение.
(5/7 - 2/3 y) * 21 = 1.

(5/7 - 2/3 y) * 21 = 1
5/7 - 2/3y = 1/21
2/3y = 5/7 - 1/21
2/3y = -14/21
y = -14/21  / 2/3
y = 7/7 = 1
Ответ. 1

[tex]( \frac{5}{7} - \frac{2}{3} y)*21=1 \\ \frac{5}{7} - \frac{2}{3} y= \frac{1}{21} \\ \frac{2}{3} y=\frac{5}{7}-\frac{1}{21} \\ \frac{2}{3} y= \frac{5*3-1}{21} \\ \frac{2}{3} y= \frac{14}{21} \\ y= \frac{14*3}{21*2} \\ y=1[/tex]

Ответ: у=1