00:01
We're asked to look at this function here, 2 cosine squared of x minus cosine of x, or you can write it as cosine of x times 2 cosine of x minus 1.
00:11
It's a little easier this way because we can see clearly that this function is 0 whenever cosine is 0 or cosine is 1⁄2.
00:20
And those happen here at 2 pi over 3, at pi over 2, and then at let's see here.
00:33
And this is then pi over, now this is two pi over, three pi over two and four pi.
00:45
That's three pie over two and four pi over three.
00:51
This is pi over two pi over three.
00:56
So we need two pi, two pi divided by minus two pi over three.
01:01
That's four pi over six.
01:05
4 pi over 3 4 pi over 3 t's right here and obviously this function is um this function is is even so it's it's symmetric about the x axis or the y axis here it's also symmetric about x equal pi um you can clearly see that here so any point we have over here we have mirro it over here taking derivative we get sign of x times one minus for a cosine of x.
01:40
So that's zero whenever sign is zero, which is any energy multiple pi, here, here, and here.
01:49
And then whenever cosine is a quarter, which is right here and here.
01:58
Taking a second derivative, another derivative, we get cosine of x minus four, cosine of 2x...