00:01
Okay, we want to write a mclaurin series for this function using a series that we already know.
00:08
All right, so remember the cosine is even, so it's the even one.
00:16
Add a dress picture to remind myself that it's the even one.
00:19
So n equals zero to infinity, minus one to the n, x to the 2n over 2n factorial.
00:27
Okay, so we want the cosine of 3x.
00:34
So everywhere i see x, i'm going to put 3x.
00:36
So i get the cosine of 3x.
00:40
So that will be n equals 0 to infinity, minus 1 to the n, 3x to the 2n over 2 in factorial.
00:54
Okay, so let's do a little fancying it up here.
00:58
Minus 1 to the n, 3 to the 2n, x to the 2n over 2 in factorial...