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Math Help - Am I or the book wrong?

  1. #1
    Senior Member Paze's Avatar
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    Am I or the book wrong?

    I solved this. All except the +/- thing?

    The question: Solve this trigonometric equation and answer in radians: Sinx=0.4

    I get 0.007+/-n*2*pi or 3.13+/-n*2*pi.

    The book claims: 0.41+n*2*pi or 2.73+n*2*pi.

    First of all I don't understand why we are getting different values. Second of all I don't understand why the book does only plus and not plus/minus. I do admit I am a little uncomfortable with trig equations and my error could be silly but I hope you can help me out.

    EDIT: Whoops...I noticed in my calculation that I was using the radians to calculate to radians.. arcsin0.4 - Wolfram|Alpha

    The arcsin of 0.4 is 23 degrees not 0.45 degrees as I thought (the radians on top). So sorry for the inconvenience if anyone is answering this! (But if you are and you notice this, please answer anyways as any knowledge on the subject is needed for me!) I still don't understand the plus minus thing.
    Last edited by Paze; March 30th 2013 at 10:57 PM.
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  2. #2
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    Re: Am I or the book wrong?

    Hello, Paze!

    Solve in radians:. \sin x\,=\,0.4

    The book claims: . \begin{Bmatrix}0.41+2\pi n \\ 2.73+2\pi n \end{Bmatrix}

    I don't understand why the book does only plus, and not plus/minus.

    The n they use is traditionally defined to be an integer,
    . . a positive or negative whole number.

    Thanks from Paze
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  3. #3
    Senior Member Paze's Avatar
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    Re: Am I or the book wrong?

    Yea I came to think of that later on. I just seem to remember it being +/- for some reason...
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