\[5bc^{2} + bc = bc\left( 5c^{2 - 1} + 1 \right) =\]
\[= bc(5c + 1)\]
\[Проверка:\ bc(5c + 1) =\]
\[= 5bc^{1 + 1} + bc = 5bc^{2} + bc\]
\[5bc^{2} + bc = 5bc^{2} + bc\]
\[\Longrightarrow верно.\]