00:01
And there's a couple ways you can do this problem, but the first thing i would do is acknowledge that we're in quadrant 1, where x is given to you here, and i know this is 2 and this is 3, because they tell me cosine of x equals 2 over 3, which if you follow sokatoa, cosine is adjacent over hypotenuse.
00:24
Because now what i can do is the pythagorean theorem.
00:27
I'll just use b for this value is equal to.
00:31
To 3 squared, well 2 squared is 4.
00:34
So subtract 4 over 9 minus 4 equals 5.
00:38
So this value would be the square of 5.
00:41
So the reason why i would go through that work is now i know sine of x is equal to opposite over hypogneuse, root 5 over 3.
00:51
And now i'm ready to figure out what sign of 2x is, because i have the formula sheet memorized to sine of x cosine of x, because now now i can say it's 2, sine of x is root 5 over 3.
01:06
The cosine is 2 over 3.
01:10
So i would just do 2 times 2 is 4, and just leave it as 4 root 5 over 3 times 3 is 9...