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Math Help - Trigonometry

  1. #1
    Member helloying's Avatar
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    Trigonometry

    1)
    2cosx-sinx=3/2cosx+sinx
    solve all possible ans of x.

    2) I got cosx=-1 and 0.4
    i am suppose to find all possible ans of x.
    i got 66.4 and 293.6 for the 0.4 already.
    but how to slove for the -1? the reference angle is 0 and since cos is negative, it should be in the 2nd and 3rd quarant. and thus i got 90 and 180. however the ans is only 180. why?
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  2. #2
    MHF Contributor
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    #1

    Do you mean

    2 \cos(x) - \sin(x) = \frac{3}{2} \cos(x) + \sin(x)

    or

    2 \cos(x) - \sin(x) = \frac{3}{2 \cos(x) + \sin(x)}

    or something else?

    #2

    cos(90) = 0

    Are you to find ALL solutions? Perhaps the Domain is restricted in some way?

    Check your definitions. Are the coordinate axes technically IN the various quadrants?
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  3. #3
    Member helloying's Avatar
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    i mean the second option
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  4. #4
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by helloying View Post
    1)
    2cosx-sinx=3/2cosx+sinx
    solve all possible ans of x.

    2) I got cosx=-1 and 0.4
    i am suppose to find all possible ans of x.
    i got 66.4 and 293.6 for the 0.4 already.
    but how to slove for the -1? the reference angle is 0 and since cos is negative, it should be in the 2nd and 3rd quarant. and thus i got 90 and 180. however the ans is only 180. why?
    Because cos(180) = -1 and cos(90) = 0. See this site and look just beneath the applet that graphs the cosine function (though this works just as well). There is a graph of y = cos(x) drawn in the "Did you notice" section.

    -Dan
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  5. #5
    MHF Contributor
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    Quote Originally Posted by helloying View Post
    i mean the second option
    When there is a question, there is also a wonderful opportunity to provide some information about your efforts and your thoughts about solvign the problem.

    I offer another opportunity for you to show your work and share your thoughts.
    Last edited by TKHunny; July 17th 2008 at 09:11 AM.
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  6. #6
    Member helloying's Avatar
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    help me please! Trigonometry

    12 cos x - 5 sin x = R cos (x + 22.6)

    solve x in range 0 to 360 degrees
    (12 cos x- 5 sin x)^2

    Also, find the max and min value of eqn.

    Kindly explain it clearly because I actually got an explanation from somewhere but it is not clear. Thank you greatly for your help.God bless you.
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  7. #7
    Member helloying's Avatar
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    sorry post in wrong place

    i wanted to post it in new thread but accidentally post it here. i have posted it in another new thread already.
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