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Math Help - Cosine addition formula bump in the road.

  1. #1
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    Cosine addition formula bump in the road.

    Hi guys,

    I'm reading up on the proof for the addition formula for cosine in my precal book. But I'm actually having a bit of trouble with a more elementary issue. It's simply what the steps are to expanding:

    (cos t - cos s)^2

    to

    cos^2 t - 2cos s cos t + cos^2 s

    I've been looking for the answer but unfortunately my elementary algebra textbook is back at home and I'm at work now. Any enlightenment is appreciated.
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  2. #2
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    Quote Originally Posted by DannyMath View Post
    Hi guys,

    I'm reading up on the proof for the addition formula for cosine in my precal book. But I'm actually having a bit of trouble with a more elementary issue. It's simply what the steps are to expanding:

    (cos t - cos s)^2

    to

    cos^2 t - 2cos s cos t + cos^2 s

    I've been looking for the answer but unfortunately my elementary algebra textbook is back at home and I'm at work now. Any enlightenment is appreciated.
    (a-b)^2 = (a-b)(a-b) = a^2 - ab - ab + b^2 = a^2 - 2ab + b^2
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  3. #3
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    Oh thank goodness. I knew it had something to do with double brackets and FOIL. Thanks so much
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