Core Maths 4: Trig identity using double angle formulae

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  1. jackie11's Avatar
    1 11-06-2012  12:14
    • Adored and Respected Member
    • Location: Suffolk (moving to London sep 2013)
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    Core Maths 4: Trig identity using double angle formulae
    Hi there

    Please could someone tell me if I am going the right way about this;







    Many thanks
    Jackie
  2. BabyMaths's Avatar
    2 11-06-2012  12:24
    • Peer Of The TSR Realm
    • Posts: 1,574
    Re: Core Maths 4: Trig identity using double angle formulae
    You started off fine with \cos(4\theta)=\cos^2 2\theta - \sin^2 2\theta.

    Now just substitute 1-\cos^2 2\theta for the \sin^2 2\theta and it's finished.
  3. Lord of the Flies's Avatar
    3 11-06-2012  12:29
    • The foul fiend Flibbertigibbet
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    Re: Core Maths 4: Trig identity using double angle formulae
    Look at the question. Then look at what you have under 8a) on the first page.
  4. Dan12's Avatar
    4 11-06-2012  12:30
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    Re: Core Maths 4: Trig identity using double angle formulae
    cos4 theta = cos squared 2 theta - sin squared 2 theta
    change the sin squared 2 theta to 1 - cos squared 2 theta
    now simplify and you get the answer
  5. Lord of the Flies's Avatar
    5 11-06-2012  12:35
    • The foul fiend Flibbertigibbet
    • Location: Paris, France
    Re: Core Maths 4: Trig identity using double angle formulae
    ... You are aware that \cos 2\theta\cos 2\theta \equiv \cos^2\ 2\theta right?
  6. jackie11's Avatar
    6 11-06-2012  12:55
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    Re: Core Maths 4: Trig identity using double angle formulae
    (Original post by Lord of the Flies)
    ... You are aware that \cos 2\theta\cos 2\theta \equiv \cos^2\ 2\theta right?
    Nope, but I am now
  7. jackie11's Avatar
    7 11-06-2012  12:56
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    • Location: Suffolk (moving to London sep 2013)
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    Re: Core Maths 4: Trig identity using double angle formulae
    OK thank you all!!!
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