Đáp án:
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Giải thích các bước giải:
${\rm a)}\,8^5+2^{11}\\=\left(2^3\right)^5+2^{11}\\=2^{15}+2^{11}\\=2^{11}.(2^4+1)\\=2^{11}.17\ \vdots\ 17\\\Rightarrow 8^5+2^{11}\ \vdots\ 17\\{\rm b)}\,69^2-69.5\\=69.(69-5)\\=69.2.32\ \vdots\ 32\\\Rightarrow 69^2-69.5\ \vdots\ 32\\{\rm c)}\,8^7-2^{18}\\=\left(2^3\right)^7-2^{18}\\=2^{21}-2^{18}\\=2^{18}.(2^3-1)\\=2^{17}.14\ \vdots\ 14\\\Rightarrow 8^7-2^{18}\ \vdots\ 14$
