00:01
So here's another half angle formula.
00:03
So let me write down the formula plus or minus a square root of 1 plus cosine of theta all over 2.
00:13
So if you didn't know as a half angle formula, it's because a cosine of pi over 12 is not on the unit circle.
00:21
But you can rewrite this as cosine of pi over 6 divided by 2.
00:27
Because if you divide by a whole number, you stick that into the denominator 6 times 2 is 12.
00:31
Or you can just believe me.
00:34
So in our formula, where you have a theta, you're going to put pi over six, which we do know on the unit circle.
00:44
Pye over six on the unit circle is right here.
00:48
That's the ordered pair root 3 over 2, one half...