0:00
All right.
00:02
There's got to be some familiarity with the unit circle in order to get this problem correct.
00:06
So you should know that 5 pi over 4 is over here in the quadrant 3.
00:13
And that's the ordered pair negative root 2 over 2, negative root 2 over 2.
00:19
And when they ask you for cosine of 5 pi over 4, they're asking for the x coordinate is cosine.
00:27
So your correct answer is negative root 2 over 2.
00:31
As we go to the next problem for letter b, we're looking at 8 pi over 3.
00:38
Well, that's not on the unit circle, but that's just saying do a full revolution would be 6 pi over 3.
00:47
And then right here would be 7 pi over 3.
00:50
We don't want that either.
00:51
But it might help you understand why we're over here at 8 pi over 3.
00:58
And that's the ordered pair negative 1ā2, root 3 over 3.
01:02
2.
01:03
So let me go ahead and give you a cosine of 8 pi over 3 is equal to negative 1 half...