00:01
We're given sine theta is equal to 2 over 3, where the angles in between pi over 2 and pi.
00:05
So drawing this out in standard position first, we know it's in the second quadrant.
00:10
The angle theta would have an opposite side of 2 and a hypotenuse of 3.
00:15
So we need to figure what the adjacent side is before we proceed.
00:19
So we have x squared plus 2 squared equals 3 squared.
00:23
X squared would be equal to 9 minus 4.
00:26
So x would be equal to root 5.
00:28
But given that this x is going to the left on the x axis it would have to be negative root 5 so part a of this problem is asking us to find the value for sine 2 theta so sine 2 theta is equal to 2 sine theta cost theta and we have both those ratios now sign theta is 2 over 3 and cost theta is adjacent over hypotenuse so negative root 5 over 3.
01:01
This will give us negative 4 root 5 over 9.
01:06
So that's the value for sine 2 theta.
01:09
Part b, we want the value for cost 2 theta.
01:13
And we have three choices here.
01:15
Given that we have sine theta provided for us, i'm going to pick the last option.
01:21
This is equal to 1 minus 2 sine squared theta.
01:26
And sine squared theta is the same thing as sine theta all squared...