Answer
$$(v+w)\cdot v-(v-w)\cdot w= \|v\|^2+\|w\|^2.$$
Work Step by Step
Using the properties of the dot product, we have
$$(v+w)\cdot v-(v-w)\cdot w\\
=v\cdot v +v\cdot w-v\cdot w+w\cdot w\\
=v\cdot v+w\cdot w= \|v\|^2+\|w\|^2.$$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.