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Math Help - Help with sum and difference identities, please!

  1. #1
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    Help with sum and difference identities, please!

    Hi there.

    We learned in calc the sum and difference identities:



    For the most part it's not too bad, but I'm confused on a couple of problems in my book.

    What would tan(a-b) be if sin a = .67, cos a = .74, sin b =.13 and cos b =-.99

    The cos of b, if you notice, is negative.



    how do I find tan(a + pi)?


    what's cos (a + pi/3)?



    and what's sin (pi/6 - a)?


    Thanks a lot!
    Last edited by gobbajeezalus; December 7th 2008 at 09:02 AM.
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  2. #2
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    Hello,
    Quote Originally Posted by gobbajeezalus View Post
    Hi there.

    We learned in calc the sum and difference identities:



    For the most part it's not too bad, but I'm confused on a couple of problems in my book.

    What would tan(a-b) be if sin a = .67, cos a = .74, sin b =.13 and cos b =-.99
    Remember that \tan(x)=\frac{\sin(x)}{\cos(x)}
    So with the information given, calculate \tan(a) and \tan(b) and substitute in the formula you're given for \tan(a-b)

    The cos of b, if you notice, is negative.
    it doesn't matter :P

    how do I find tan(a + pi)?
    make x=a \quad y=\pi

    what's cos (a + pi/3)?
    make x=a \quad y=\pi/3

    and what's sin (pi/6 - a)?
    make x=\pi/6 \quad y=a in the sin(x-y) formula.


    Now, for these last 3 values, you have to know specific values of trigonometric functions, at some points.

    They're "listed" here : http://everobotics.org/projects/robo...UnitCircle.gif
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