\[\boxed{\text{1039.}\text{\ }еуроки - ответы\ на\ пятёрку}\]
\[\textbf{а)}\ (2n + 3)(3n - 7) -\]
\[- (n + 1)(n - 1) = 6n^{2} - 14n +\]
\[+ 9n - 21 - n^{2} + 1 =\]
\[= 5n^{2} - 5n - 20 =\]
\[= 5 \cdot \left( n^{2} - n - 4 \right) \Longrightarrow делится\ \]
\[на\ 5.\]
\[\textbf{б)}\ (7n + 8)(n - 1) +\]
\[+ (3n - 2)(n + 2) =\]
\[= 7n^{2} - 7n + 8n - 8 + 3n^{2} +\]
\[+ 6n - 2n - 4 = 10n^{2} +\]
\[+ 5n - 12 =\]
\[= 5 \cdot \left( 2n^{2} + n - 2 \right) - 2 \Longrightarrow не\]
\[\ кратно\ 5.\ \]