# Strange vectors question very short

1. Oct 27, 2013

### phospho

Question http://gyazo.com/17223631de9dfcbcca00f6b3f8758cb9

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?

2. Oct 27, 2013

### haruspex

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.