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Math Help - Trig question

  1. #1
    Newbie hymnseeker's Avatar
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    Trig question

    Solve Sin2x=Cos2x

    I know:

    Sin2x=2SinxCosx

    I also know:

    Cos2x=cos²x-sin²x
    Cos2x=2cos²x-1
    Cos2x=1-2sin²x

    How do I rearrange and solve?

    Thanks x
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  2. #2
    Senior Member euclid2's Avatar
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    Quote Originally Posted by hymnseeker View Post
    Solve Sin2x=Cos2x

    I know:

    Sin2x=2SinxCosx

    I also know:

    Cos2x=cos²x-sin²x
    Cos2x=2cos²x-1
    Cos2x=1-2sin²x

    How do I rearrange and solve?

    Thanks x
    sin2x=2sincosx is the double angle formula, which ones do you wish to solve?
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  3. #3
    Newbie hymnseeker's Avatar
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    Sorry, the question was:

    Solve Sin2x=Cos2x
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  4. #4
    Senior Member euclid2's Avatar
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    Quote Originally Posted by hymnseeker View Post
    Sorry, the question was:

    Solve Sin2x=Cos2x
    Ok. Try using SinA/CosA = TanA

    Then Tan2x=1 and 2x = 45 degrees plus the solution in the third fifth and seventh quadrant

    Does this help atol?
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  5. #5
    Newbie hymnseeker's Avatar
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    Thanks man.

    Got it.

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  6. #6
    Senior Member euclid2's Avatar
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    Quote Originally Posted by hymnseeker View Post
    Thanks man.

    Got it.

    No problem, just make sure for these types of questions that you know
    1.sine is positive in quads 1 and 2
    2.cosine is positive in 1 and 4
    3.tangent is positive in 1 and 3
    4.sin0=sin180=0
    5.cos90=cos270=0
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