finding and angle x in radians?

**captaintoast87** · February 28th 2009, 06:38 AM

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

**e^(i*pi)** · February 28th 2009, 06:59 AM

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 $8\pi + \frac{\pi}{3} = \frac{25\pi}{3}$

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