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Thread: i Have tried this sum,,,but couldnt. can you help

  1. #1
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    i Have tried this sum,,,but couldnt. can you help

    Thank you in advance.
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  2. #2
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    Re: i Have tried this sum,,,but couldnt. can you help

    this is a very simple sum
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  3. #3
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    Re: i Have tried this sum,,,but couldnt. can you help

    What have you tried? Did you start with the sum of angles formula? What about $\sin^2 x + \cos^2 x = 1$? If you use that, you should be able to find at least a possible $f(x)$.
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    Re: i Have tried this sum,,,but couldnt. can you help

    This is what i got
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  5. #5
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    Re: i Have tried this sum,,,but couldnt. can you help

    Good start. You did not apply the sum of angles formula for sine correctly. The sum of angles formula is:

    $$\sin(\alpha+\beta) = \sin \alpha \cos \beta + \cos \alpha \sin \beta$$

    Applying that to $\sin(3x)$ gives:

    $$\sin(3x) = \sin(2x)\cos x + \cos(2x)\sin x$$

    Now, you can apply the double angle formula for $\sin (2x) = 2\sin x \cos x$ and for $\cos(2x) = \cos^2 x - \sin^2 x = 2\cos^2 x - 1 = 1-2\sin^2 x$.
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  6. #6
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    Re: i Have tried this sum,,,but couldnt. can you help

    I used sin C- sin D
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    Re: i Have tried this sum,,,but couldnt. can you help

    Quote Originally Posted by IamSujith View Post
    I used sin C- sin D
    Oh, my mistake. I missed that. Good point. In that case, I'm not seeing it. What makes you think this is possible?
    Last edited by SlipEternal; Jul 18th 2018 at 07:52 AM.
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  8. #8
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    Re: i Have tried this sum,,,but couldnt. can you help

    Its a question from a final Advance level school paper. Then there must be a way.
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  9. #9
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    Re: i Have tried this sum,,,but couldnt. can you help

    Wolfram|Alpha: Computational Intelligence

    According to Wolframalpha, there are no real solutions. Is it possible the problem statement has a typo? Maybe a plus should be a minus or vice versa?
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