21. (\(\frac{2}{7} - \frac{3}{6}\) - (\(\frac{1}{2}\))) \(\cdot (-7)\)

Решение:

\( \left( \frac{2}{7} - \frac{3}{6} - \frac{1}{2} \right) \cdot ( -7 ) = \left( \frac{2}{7} - \frac{1}{2} - \frac{1}{2} \right) \cdot ( -7 ) = \left( \frac{2}{7} - 1 \right) \cdot ( -7 ) = \left( \frac{2-7}{7} \right) \cdot ( -7 ) = \frac{-5}{7} \cdot ( -7 ) = 5 \)

Ответ: 5