00:01
On this problem, we would like to find the cosine of theta minus fee.
00:07
Now we've been given that the cosine of theta is 3 over 5, and the tangent of fee is negative root 3.
00:22
Now, the cosine of theta, i'm sorry, the cosine of theta minus fee, our identity here is equal the cosine of theta times the cosine of fee plus the sign of theta times the sign of fee.
00:38
Now we don't know the cosine of fee, we don't know the sine of theta, we don't know the sign of fee, but we know how to find these.
00:45
Now if the cosine of theta is equal to three -fiths, we start here.
00:49
We know that we are in the second quadrant.
00:56
The cosine is, i'm sorry, we were in the fourth quadrant here.
01:00
Let's look at the wrong one.
01:01
We were in the fourth product for the cosine of theta is three -fifths.
01:08
So we're down here.
01:10
Sorry by that.
01:11
So this is three.
01:12
This is five.
01:14
Using the pythagorean theorem, we'll get the other side is four.
01:16
Since it's in the fourth quadrant, it's negative four.
01:20
So we know the cosine of theta is 3 over 5...