Вопрос:

Ответ:

\[7x^{2} - 147x = 0\]

\[7x(x - 21) = 0\]

\[1)\ 7x = 0\]

\[x = 0.\]

\[2)\ x - 21 = 0\]

\[x = 21.\]

\[21 - 0 = 21.\]

\[Ответ:21.\]