Đáp án:
$\begin{array}{l}a. \ (4x-1)^3=27\\\rightarrow (4x-1)^3=3^3\\\rightarrow 4x-1=3\\\rightarrow 4x=4\\\rightarrow x=1\\\text{Vậy} \ x=1\\b. \ 2^{x-1}+3^3=5^2+2\times5\\\rightarrow 2^{x-1}+27=25+10\\\rightarrow 2^{x-1}+27=35\\\rightarrow 2^{x-1}=8\\\rightarrow 2^{x-1}=2^3\\\rightarrow x-1=3\\\rightarrow x=4\\\text{Vậy} \ x=4\end{array}$