Giải thích các bước giải:
Em tách hỏi từng câu thôi nhé
\(\begin{array}{l}
7)\left( {2n + 5} \right)\, \vdots \,\left( {n + 1} \right)\\
\Rightarrow \left( {2n + 2 + 3} \right)\, \vdots \left( {n + 1} \right)\\
\Rightarrow \left( {2\left( {n + 1} \right) + 3} \right)\, \vdots \,\left( {n + 1} \right)\\
Vi\,2\left( {n + 1} \right)\, \vdots \,\left( {n + 1} \right) \Rightarrow 3 \vdots \left( {n + 1} \right)\\
\Rightarrow \left( {n + 1} \right) \in U\left( 3 \right) = \left\{ {1;3} \right\}\\
\Rightarrow n \in \left\{ {0;2} \right\}\\
8)\,\,A = \dfrac{{{{\left( {{4^2}} \right)}^4}.{{\left( {{9^2}} \right)}^3}}}{{{9^5}{{.4}^9}}} = \dfrac{{{4^8}{{.9}^6}}}{{{9^5}{{.4}^9}}} = \dfrac{9}{4}\\
B = \dfrac{{{{\left( {{5^3}} \right)}^2}.{{\left( {72:9} \right)}^3}}}{{{4^3}.{{\left( {25:5} \right)}^5}}} = \dfrac{{{5^6}{{.8}^3}}}{{{4^3}{5^5}}}\\
= \dfrac{{{{5.4}^3}{{.2}^3}}}{{{4^3}}} = 5.8 = 40
\end{array}\)
