7. $\vec{b}_{6}$.

The above text has been translated into English, maintaining the original text's line breaks and format.
7. For a regular octagon $A_{1} A_{2} A_{3} \cdots A_{7} A_{8}$ centered at the origin, if we denote $\overrightarrow{a_{0}}=\overrightarrow{A_{8} A_{1}}, \vec{a}_{i}=$ $\overrightarrow{A_{i} A_{i+1}}(i=1,2, \cdots, 7), \vec{b}_{j}=\overrightarrow{O A_{j}}(j=1,2, \cdots, 8)$, then $\vec{a}_{2}+\vec{a}_{5}+\overrightarrow{b_{2}}+$ $\vec{b}_{5}+\vec{b}_{7}=$ $\qquad$