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Math Help - Trig Prove

  1. #1
    Member srirahulan's Avatar
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    Srilanka
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    Question Trig Prove

    \mbox{if}\ A+B+C=\pi\ \mbox{then prove,}\ sin2A+sin2B+sin2C=4sinAsinBsinC
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  2. #2
    Newbie
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    May 2012
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    silchar
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    Re: Trig Prove

    sinn2a + sin2b = 2sin(a+b)cos(a-b)
    =2sinc{cos(a-b)}

    lhs becomes
    =2sinc{cos(a-b)} + sin2c
    =2sinc{cos(a-b) + cosc}
    =2sinc{cos(a-b) - cos(a+b)}
    =4sina.sinb.sinc=rhs
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