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Thread: trigonometric multiple angle formula

  1. #1
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    trigonometric multiple angle formula

    Hi could I get Help with this question really struggling I need to use angle formula to show cos^2x=1/2 (cos2x-1).
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  2. #2
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    Re: trigonometric multiple angle formula

    Which "angle formula" are you supposed to use? Are you talking about the double angle formula for cosine?

    $\displaystyle \cos(2x) = 2\cos^2 x -1$

    Is that the "angle formula" you are referring to? If it is, then add 1 to both sides. Then divide both sides by 2.
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  3. #3
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    Re: trigonometric multiple angle formula

    I haven't been given one I've been told to use one of the multiple angle formula as to which one to use I'm not quite sure
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  4. #4
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    Re: trigonometric multiple angle formula

    How about:
    $\cos(\alpha + \beta) = \cos \alpha \cos \beta - \sin \alpha \sin \beta$

    Let $\alpha = x$ and $\beta=x$. See what you get on the left and right sides.
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  5. #5
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    Re: trigonometric multiple angle formula

    Quote Originally Posted by Nadir View Post
    Hi could I get Help with this question really struggling I need to use angle formula to show cos^2x=1/2 (cos2x-1).
    The question is written incorrectly
    It should be $\cos^2(x)=(1/2) (\cos(2x)\large\color{red}+1)$
    Thanks from topsquark
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  6. #6
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    Re: trigonometric multiple angle formula

    Yeah I thought so I asked my teacher and he said he made a mistake with the question and it was incorrect thanks for pointing it out
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