Strange vectors question very short

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Question http://gyazo.com/17223631de9dfcbcca00f6b3f8758cb9

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?
 

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haruspex
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Question http://gyazo.com/17223631de9dfcbcca00f6b3f8758cb9

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?
The power of 2 in ## (\vec{OC} - \vec{OB})^2 ## indicates the dot product of the vector with itself, so when you expand it all the vector products are dot products.
 

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