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Math Help - compund angle formula prob

  1. #1
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    compund angle formula prob

    hello i am having trouble with a question here it is

    use an appropriate compound angle formulae to express a a single trig formula than determine an exact formula for each

    a) sin pi/4 cos pi/12 +cos pi/4 sin pi/12

    so i got most of it i put it in to the fourmla sin(x+y)=sinxcosx+cosysinx

    i solved for the right side and got square root of 3 over 2
    but for the left side i am having trouble relating pi/12 to a special triangle as it is only 15
    so far i am only able to do
    sin pi/4 cos pi/12 + cos pi/4 sin pi/12
    1/sq root of2 + blank+1/sq of root 2 + blank

    as you can see i can solve the cos pi/12 and sin pi/12 if some one could please help me and show full steps as there is the same number for the diff compund formulas so i can see how to solve thos thank you
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  2. #2
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    Re: compund angle formula prob

    Hint: sin(pi/12) = sqrt((1-cos(pi/6))/2)
    Last edited by alphabeta89; November 3rd 2012 at 07:06 AM.
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  3. #3
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    Re: compund angle formula prob

    Hi Zxcismia,
    your solution is perfect:
    sin45°cos15°+cos45°sin15°=sin(45°+15°)=sin60°=(3^0 .5)/2
    as you wrote.
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