2.$3^{x+1}+2x3^x-18x-27=0$
$\Leftrightarrow 3^x(2x+3)-9(2x+3)=0$
$\Leftrightarrow (2x+3)(3^x-9)=0$
$\Leftrightarrow x=\frac{-3}{2} hoặc x=2$
3.
$\sqrt[3]{1-x}+\sqrt{x+2}=1$
Đặt: $\left\{ \begin{array}{l} \sqrt[3]{1-x}=a\\ \sqrt{x+2}=b \end{array} \right.$
Khi đó ta có hệ$\left\{ \begin{array}{l} a+b=1\\ a^3+b^2=3 \end{array} \right.$
$\Leftrightarrow \left\{ \begin{array}{l} a=-1\\ b=2 \end{array} \right.$ hoặc $\left\{ \begin{array}{l} a=-\sqrt2\\ b=1+\sqrt2\end{array} \right.$
Kq: $x=2$ hoặc $x=1+2\sqrt2$