In triangle $ABC,$ $AB = 3$ and $AC = 5.$  Let $O$ be the circumcenter of triangle $ABC.$  Find $\overrightarrow{OA} \cdot \overrightarrow{BC}.$
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In triangle $ABC,$ $AB = 3$ and $AC = 5.$  Let $O$ be the circumcenter of triangle $ABC.$  Find $\overrightarrow{OA} \cdot \overrightarrow{BC}.$
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In triangle $ABC,$ $AB = 3$ and $AC = 5.$  Let $O$ be the circumcenter of triangle $ABC.$  Find $\overrightarrow{OA} \cdot \overrightarrow{BC}.$
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