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Math Help - Please help how can ı find (sin36)=?

  1. #1
    Newbie mialkan's Avatar
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    Please help how can ı find (sin36)=?

    Sin36=? without using calculator
    Last edited by mialkan; February 15th 2008 at 05:24 AM.
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  2. #2
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    Quote Originally Posted by mialkan View Post
    Sin36=?
    You use a calculator.

    And hey ..... what happens if you google

    sin(36 degrees)
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  3. #3
    Newbie mialkan's Avatar
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    ı know thank but I have to use summation property which is sin(72+18)=sin72.cos18+sin18.cos72 when you plug 2.sin36.cos36 isntead of sin72 but I dont know the rest of soution ı tried
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    Quote Originally Posted by mialkan View Post
    ı know thank but I have to use summation property which is sin(72+18)=sin72.cos18+sin18.cos72 when you plug 2.sin36.cos36 isntead of sin72 but I dont know the rest of soution ı tried
    \sin(36^{\text{o}}) = \frac{\sqrt{2(5 - \sqrt{5})}}{4}.

    I don't have time now to type up the derivation - maybe later. Unless someone beats me to it.
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  5. #5
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    Quote Originally Posted by mr fantastic View Post
    \sin(36^{\text{o}}) = \frac{\sqrt{2(5 - \sqrt{5})}}{4}.

    I don't have time now to type up the derivation - maybe later. Unless someone beats me to it.
    This link should give you enough information to calculate the result.

    Alternatively, the result can be got using complex numbers .....
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  6. #6
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    Quote Originally Posted by mialkan View Post
    Sin36=? without using calculator
    Start by setting \sin36^\circ=\cos54^\circ.

    Since 2\cdot18=36 & 3\cdot18=54, combine double and triple angle formulae for sine and cosine. You'll get a quadratic equation.
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  7. #7
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    Talking Hi......it's not a problem ...

    [QUOTE=mialkan;107293]Sin36=? without using calculator[/QUOTE

    For solving this problem.....At first,u consider the value of sin(210 deg)= -1/2,
    now we know that 210=36*5;
    write the equation....sin(5*36)= -1/2 & then express the equation as a function of sin(36 deg) means sin(5x) in terms of sinx....and then solve the equation...
    after solving the equation ....U will get the result.
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