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Math Help - Solving simultaneous trig and linear equations

  1. #1
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    Solving simultaneous trig and linear equations

    Solving simultaneous trig and linear equations-20.11.png
    Last edited by mr fantastic; November 20th 2009 at 01:07 PM. Reason: Changed post title
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  2. #2
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    Solution

    Dear , the solution is SO easy : first : alfa-beta = 2pi/3 => beta =alfa - 2pi/3 , cos ( beta ) = cos ( alfa - 2pi/3 )

    as we know cos ( a - b ) = cos a cos b + sin a sin b

    => cos ( alfa - 2pi/3 ) = cos (alpha ) cos ( 2pi/3 ) + sin ( alfa ) sin ( 2pi/3 )

    => you can calculate cos alpha wich is square root ( 1 - sin ( alpha ) ^ 2 ) becarefull you have to take the negative value becoz alpha betwiin pi and 3 pi / 2 and in this region the cos in negative cos alpha = - ( square root 7 ) / 7

    the final answer is : cos ( beta ) = (sqr root 3 ) / 14 - 6/7

    note : check again i solved it very fast
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  3. #3
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    The answer isn't correct, doesn't matter, cause I figured it out by myself
    here 's correct answer ( Thanks anyway)
    Attached Thumbnails Attached Thumbnails Solving simultaneous trig and linear equations-21.11.jpg  
    Last edited by livmed; November 20th 2009 at 02:27 PM.
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  4. #4
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    Quote Originally Posted by livmed View Post
    The answer isn't correct, doesn't matter, cause I figured it out by myself
    here 's correct answer ( Thanks anyway)
    it is about the method not about the answer
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