<p>Sorry to bother again, but I have another question. The question is to find the derivative of y=cos3x. I know that the answer is -3sin3x. However I got that answer because I used the shortcut method of finding derivatives. My teacher wants to use the limits way to figure out the derivative and I am stuck on how to solve it. Thanks</p>
<p>go here <a href="http://whyslopes.com/Calculus-Introduction/Derivatives_sine_cosine03.html%5B/url%5D">http://whyslopes.com/Calculus-Introduction/Derivatives_sine_cosine03.html</a></p>
<p>same principle except you have to account for the 3x</p>
<p>thanks a lot it'sGr82beAGator. That site was very helpful and I solved the problem.</p>