7. The minimum value of the function $y=\sqrt{x^{2}+2 x+2}+\sqrt{x^{2}-2 x+2}$ is $\qquad$ .
$$
\begin{array}{l}
\text { II.7.2 } \sqrt{2} . \\
\begin{aligned}
y \geqslant 2 \sqrt[4]{\left(x^{2}+2 x+2\right)\left(x^{2}-2 x+2\right)} \\
\quad=2 \sqrt[4]{x^{4}+4} \geqslant 2 \sqrt{2} .
\end{aligned}
\end{array}
$$

The equality holds if and only if $x=0$, that is, when $x=0$, $y$ attains its minimum value of $2 \sqrt{2}$.