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Math Help - Help proving this expression is equal..

  1. #1
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    Help proving this expression is equal..

    Prove that [sin x + cos x]^2 = 1 + sin 2x
    Last edited by Manizzle; November 26th 2008 at 06:21 PM.
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  2. #2
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    Quote Originally Posted by Manizzle View Post
    Prove that [sin x + cos x] = 1 + sin 2x
    I think you mean ...

     (\sin{x} + \cos{x})^2 = 1 + \sin(2x)
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    Senior Member vincisonfire's Avatar
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    If that's not what he means then his book must be wrong.
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    yes i'm sorry thats what i meant, my superscript didn't work with the font i had on here sorry guys
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  5. #5
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     (\sin{x} + \cos{x})^2 = 1 + \sin(2x)

    square the left side ...

    \sin^2{x} + 2\sin{x}\cos{x} + \cos^2{x}

    rearrange a bit ...

    (\sin^2{x} + \cos^2{x}) + 2\sin{x}\cos{x}

    now, you should know what the sum of the first two terms is ... also, look up the double angle formula for sine to deal with the last term.
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