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    How would you solve this without a calculator:

    cosx + cos3x = sinx +sin3x

    Between 0 and 2pi
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    (Original post by pippabethan)
    How would you solve this without a calculator:

    cosx + cos3x = sinx +sin3x

    Between 0 and 2pi
    Apply double angle would be the obvious way. I don't have time at the moment so I can't provide you with an alternative. Try to get it in terms of a single trig function with double angle.
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    use the second from bottom and fourth from bottom of these relationships:*

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    Use the factor formulae
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    This is what I've got so far. I know that sin3x can be simplified in terms of sinx only but I can't see how that would help. Any hints?
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    (Original post by pippabethan)
    This is what I've got so far. I know that sin3x can be simplified in terms of sinx only but I can't see how that would help. Any hints?
    You're making it way too complicated - look at the formulae provided by thebear in post #3. These should also be in your formula book - ways of rewriting sin A + sin B and cos A + cos B
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    I had a go but it got a bit nasty & complicated
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