00:01
Okay, we want to evaluate this integral, cosine squared x over 2 dx.
00:06
And that looks kind of hard, but they tell us to use a trigonometric identity, which is great.
00:11
And the one that we're going to use is actually cosine 2 theta.
00:17
There's three forms of this.
00:19
I actually recommend memorizing all three forms.
00:24
You can get them all via just substituting using the trig identity cosine squared theta plus sine square theta equals one.
00:34
That's what all of these are related by.
00:36
So if like if i plug that in for one here, i would get from there to there.
00:44
But they're also useful that i actually do recommend memorizing all of them.
00:49
And i don't recommend memorizing a lot of stuff.
00:52
Okay, so we're going to be using some form of the top one.
00:58
And i'm going to put in an x over two for theta...