00:01
Okay, so first we're starting with the sign of 120 degrees.
00:05
Now, normally we can evaluate this using our unit circle, et cetera, but we're trying to practice our identities here.
00:13
So we're going to use the sign of a plus b.
00:17
And in this case, the easiest angles to work with are 90 degrees and 30 degrees.
00:23
Now, there's a lot of different ways to get there, but this one's the easy one.
00:26
Most straightforward.
00:29
So sign of the first, cosine of the first.
00:33
Second plus cosine of the first sign of the second.
00:40
So the sign at 90 degrees that's up here is going to be one.
00:45
The cosine at 30 degrees is going to be root 3 over 2 from your unit circles, plus the cosine at 90 degrees is 0, and the sign at 30 degrees is 1 half.
00:57
This is going to become 0 and 1 times root 3 over 2 is root 3 over 2.
01:04
The second question is asking you to evaluate the cosine of 240 degrees...