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Math Help - how to remmember these trigonometric formulas

  1. #1
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    how to remmember these trigonometric formulas

    Table of Trigonometric Identities
    sum to product formulas part
    i am looking for a logical way of remmembering them
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  2. #2
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    Quote Originally Posted by transgalactic View Post
    Table of Trigonometric Identities
    sum to product formulas part
    i am looking for a logical way of remmembering them
    I'm not sure there's many shortcuts for this. It's just a case of strapping down and memorising them. Write them out a few hundred times. Derive them a few hundred times as knowing where they come from can help. Write them on paper and pin them to the ceiling above your bed or whatever.

    Personally, I find it best just to remember quick versions of the derivations, that way I don't have to memorising anything except the original equations.
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  3. #3
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    Hello transgalactic
    Quote Originally Posted by transgalactic View Post
    Table of Trigonometric Identities
    sum to product formulas part
    i am looking for a logical way of remmembering them
    When I learnt these (about 200 years ago) I was recommended to use words, not symbols. After all, that's the way most of us learn our tables. It's a question of establishing a rhythm in your head. I've always recommended my students to learn them this way.

    It goes like this:
    Sine plus sine is twice sine half-sum, cosine half-difference.
    The next one swaps the sine and cosine around on the RHS:
    Sine minus sine is twice cos half-sum, sine half-difference.
    The next is the line of all cosines:
    Cos plus cos is twice cos half-sum, cos half-difference.
    The last one you remember, simply because it's different from all the rest; plus, being cosines it's the wrong way round. (Cosine is always awkward - when you differentiate it, for instance, you get a minus sine - pun intended.)
    Cos minus cos is twice sine half-sum, sine half-difference reversed.
    Just repeat these words over and over - you'll end up remembering them, just like learning a poem. Take my advice - don't try to learn them by writing them down using symbols and letters.

    Grandad
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  4. #4
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    what rithm to use

    like hiphop/ or like acid trance or like country rithm



    it doesnt rihm at all

    "Sine plus sine is twice sine half-sum, cosine half-difference"
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  5. #5
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    its not going to be like this
    <br />
a_{-n} = \frac{1}{2\pi}\int_{-\pi}^{\pi} \! f(t)e^{-i(-n)t} \, dt<br />
    you forgot to put a line above the f(x)
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