\[\boxed{\text{691\ (691).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ (c - 8)(c + 3) = c^{2} - 5c - 24\ \]
\[c^{2} + 3c - 8c - 24 = c^{2} - 5c - 24\]
\[c^{2} - 5c - 24 = c^{2} - 5c - 24\]
\[Верно.\]
\[\textbf{б)}\ (m - 4)(m + 7) =\]
\[= m^{2} + 3m - 28\]
\[m^{2} + 7m - 4m - 28 =\]
\[= m^{2} + 3m - 28\ \]
\[m^{2} + 3m - 28 = m^{2} + 3m - 28\]
\[Верно.\]