Cho A=2^a.(2^a.2^a^2.2^a^3...2^a^9

* Hướng dẫn giải

Đáp án B

Ta có:

$S=a+a^2+\mathrm{...}+a^9\Rightarrow a.S=a^2+a^3+\mathrm{...}+a^{10}\Rightarrow \left(a-1\right)S=a^{10}-a$

$A=2^a.{\left(2^S\right)}^{a-1}=2^{S.\left(a-1\right)+a}=2^{a^{10}}=2^{2^5}\Rightarrow a^{10}=2^5\Rightarrow a^{10}={\left(\sqrt{2}\right)}^{10}\Rightarrow a=\sqrt{2}$