Answer
$|u-v|^2=|u|^2+|v|^2-2u\cdot v$
Work Step by Step
$|u-v|^2=(u-v)(u-v)=u\cdot u-u\cdot v-v\cdot u+v\cdot v=|u|^2+|v|^2-2u\cdot v$
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