# finding and angle x in radians?

• Feb 28th 2009, 07:38 AM
captaintoast87
finding and angle x in radians?
Find an angle x in radians such that 8pi<x<9pi and cosx=1/2

What is this question asking for? I came up with pi/3, but I don't think that's in between 8 and 9 pi. Can anyone explain? Thanks
• Feb 28th 2009, 07:59 AM
e^(i*pi)
Quote:

Originally Posted by captaintoast87
Find an angle x in radians such that 8pi<x<9pi and cosx=1/2

What is this question asking for? I came up with pi/3, but I don't think that's in between 8 and 9 pi. Can anyone explain? Thanks

Remember that $\cos{x}$ is periodic with a a period of $2\pi$ which means you get your original answer of $\frac{\pi}{3}$ and add 4 lots of $2\pi$ (this is 4 periods) to give you an answer of $8\pi + \frac{\pi}{3} = \frac{25\pi}{3}$