\[\boxed{\text{854.}\text{\ }еуроки - ответы\ на\ пятёрку}\]
\[\textbf{а)}\ b² + 20b + 100 = (b + 10)²\]
\[*\ = 100\]
\[\textbf{б)}\ b² + 14b + 49 = (b + 7)²\]
\[*\ = b^{2}\]
\[\textbf{в)}\ 16x² + 24xy + 9y² = (4x + 3y)²\]
\[*\ = 9y^{2}\]
\[\textbf{г)}\ 9p² - 42pq + 49q^{2} = (3p - 7q)²\ \]
\[*\ = 9p^{2}\]