Đáp án:
Giải thích các bước giải:
\(\begin{array}{l}A){\rm{ }}A = 5.7.11.13.17 + 21\\\,\,\,\,\,\,\,\,A = \,5.7.11.13.17 + 7.3\\\,\,\,\,\,\,\,\,A = \,7.\left( {5.11.13.17 + 3} \right)\\ \Rightarrow A\,\,\,la\,\,hop\,\,so\end{array}\)
\(\begin{array}{l}B){\rm{ }}B = 3.5.7.9.11.17 + 13.15.19\\\,\,\,\,\,\,B = \,15.\left( {7.9.11.17 + 13.19} \right)\\ \Rightarrow B\,\,\,la\,\,hop\,\,so\end{array}\)
\(\begin{array}{l}c)\,\,C = {10^8} + 8\\\,\,\,\,\,\,\,C = 2.\left( {{{5.10}^7} + 1} \right)\\ \Rightarrow C\,\,la\,\,hop\,so\end{array}\)
\(\begin{array}{l}d)\,{2^6} - 31.2 = 64 - 62 = 2\\ \Rightarrow \,\,\,la\,\,so\,\,\,nguyen\,to\end{array}\)
