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Math Help - Need tips

  1. #1
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    Need tips

    hello this maybe is wrong to ask but i wounder if any1 got a tips for a page that can help u if u got problem with geometry :/ maybe webblesion..?
    well im reading a course named analysis and got problem with this geometry basicly i havent understand this (yet) well i can give u exemple what we doing.. Calculate . The answer may not contain trigonometric functions.
    basicly we have been using calculater before but without calculate im really bad on this because i havent understand it (yet) so tips plz?
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  2. #2
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    Re: Need tips

    \arccos\left(-\frac{1}{2}\right) is the angle in the interval [0,\pi] whose cosine is -\frac{1}{2} ...

    \arccos\left(-\frac{1}{2}\right) = \frac{2\pi}{3}

    Pauls Online Notes : Algebra/Trig Review - Inverse Trig Functions
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  3. #3
    MHF Contributor MarkFL's Avatar
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    Re: Need tips

    Think of this as:

    \theta=\arccos\left(-\frac{1}{2} \right) where 0\le\theta\le\pi

    We can rewrite the equation as:

    \cos(\theta)=-\frac{1}{2}

    What special angle in the given range makes this true?
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  4. #4
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    Re: Need tips

    Quote Originally Posted by skeeter View Post
    \arccos\left(-\frac{1}{2}\right) is the angle in the interval [0,\pi] whose cosine is -\frac{1}{2} ...

    \arccos\left(-\frac{1}{2}\right) = \frac{2\pi}{3}

    Pauls Online Notes : Algebra/Trig Review - Inverse Trig Functions
    hello skeeter!
    well -1/2 does it mean u go backway ehmm maybe bad explain but ima try explain it on a easy way because idk other way to explain, not best english...
    uk how the cloak goes, that way so it should be 0,2pi? can u also explain a litle more how u got it to 2pi/3
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  5. #5
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    Re: Need tips

    Quote Originally Posted by MarkFL2 View Post
    Think of this as:

    \theta=\arccos\left(-\frac{1}{2} \right) where 0\le\theta\le\pi

    We can rewrite the equation as:

    \cos(\theta)=-\frac{1}{2}

    What special angle in the given range makes this true?
    cos x = cos (x + 2kx)
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  6. #6
    MHF Contributor MarkFL's Avatar
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    Re: Need tips

    That's true for any x, where k is an integer.

    You are expected to know that:

    \cos\left(\frac{2\pi}{3} \right)=-\frac{1}{2}
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  7. #7
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    Re: Need tips

    ohh ok but if i would solve this problem with that formel i wouldent know how to do it.. the thing is i got problem to decide that k...
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