00:01
Okay, so we're given in this problem that cosine of theta is equal to just double checking negative 4 -fiths.
00:10
And we also know that we're in quadrant three, so let me just draw that real quick.
00:13
If you're in quadrant three, what i like to do is make the angle made with the x -axis.
00:20
So it's right here.
00:22
And cosine is adjacent over hypotenuse.
00:25
So this side will be negative four.
00:27
This side would be five.
00:27
And this is a 3, 4, 5 right triangle.
00:32
You might even call it a pythagorean triple because it's always true that 3 squared plus 4 squared equals 5 squared.
00:39
So i would encourage you to memorize that...