Math Help Web-Sites?

<p>I'm a little bit confused about some of the vector problems in my Precalc. class and was hoping that you guys might be able to suggest some math sites with helpful explanations, practice problems, etc. Thanks!</p>

<p><a href="http://www.artofproblemsolving.com%5B/url%5D"&gt;www.artofproblemsolving.com&lt;/a&gt;&lt;/p>

<p>AoPS hands down.</p>