$\begin{aligned}
& f(x)=3 \sqrt{x-2}+\sqrt{4-x} \
& x-2 \geq 0 & 4-x \geq 0 \
& \therefore x \in[2,4]
\end{aligned}$
Let x=2sin2θ+4cos2θ $\begin{aligned}
& \therefore \mathrm{f}(\mathrm{x})=3 \sqrt{2}|\cos \theta|+\sqrt{2}|\sin \theta| \
& \therefore \sqrt{2} \leq 3 \sqrt{2}|\cos \theta|+\sqrt{2}|\sin \theta| \leq \sqrt{9 \times 2+2} \
& \sqrt{2} \leq 3 \sqrt{2}|\cos \theta|+\sqrt{2}|\sin \theta| \leq \sqrt{20} \
& \therefore \alpha=\sqrt{2} \quad \beta=\sqrt{20} \
& \alpha^2+2 \beta^2=2+40=42
\end{aligned}$