00:01
Coast theta is equal to negative 4 over 5, where the angle is in between pi and 3 pi over 2.
00:05
So drawing this out in standard position, we would have an angle that's in the third quadrant.
00:10
The reference angle is theta.
00:12
The adjacent side is negative 4, and the hypotenuse is 5.
00:16
So using pythagorean theorem, we want to find y.
00:20
We got negative 4 squared plus y squared equals 5 squared.
00:25
Y squared would be 25 minus 16 and y would be equal to 3.
00:31
But it's going down.
00:33
So we would need negative 3 as our answer for y.
00:37
Now, in part a, we would like to find sine 2 theta.
00:44
So sine 2 theta is equal to 2 sine theta, coast theta, which is equal to 2 .5 theta is opposite over a hypotenuse.
00:55
Negative 3 over 5.
00:58
Coast theta is given to us negative 4 over 5.
01:01
So that gives us 24 over 25.
01:08
In part b, we want to do cos 2 theta...