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I'm talking about part ii)

if ## a = |\vec{BC}| ## then ## a^2 = (\vec{OC} - \vec{OB})^2 ## is this correct?

if we expand a^2 then we get ## a^2 = (\vec{OC})^2 - 2\vec{OC}\vec{OB} + (\vec{OB})^2 ## I don't understand, what is ## 2\vec{OC}\vec{OB}## is it the dot product or what?