Yitong Li edited untitled.tex  almost 8 years ago

Commit id: ad4c9cbac624bbf6f5c75a0053e20beac494dc33

deletions | additions      

       

In the second case, when $W$ is nonzero, then consider the unit vector $U = \frac{W}{||W||}$. Then, by the result in the question, it follows that $V = (U · V)U$. Therefore:  $$V = (U · V)U = (\frac{W}{||W||}· V)·\frac{W}{||W||}= (\frac{W·V}{W^2})·W$$  As $(\frac{W·V}{W^2})$ is a constant, so $V $V$  is a multiple of W$. $W$.