8. Given that $\alpha, \beta$ are acute angles, and
$$
\left\{\begin{array}{l}
3 \sin ^{2} \alpha+2 \sin ^{2} \beta=1, \\
3 \sin 2 \alpha-2 \sin 2 \beta=0 .
\end{array}\right.
$$

Then $\alpha+2 \beta=$ $\qquad$ .
8. $\frac{\pi}{2}$