tanjung
Help...
Prove that sin36 degrees = sqrt[10  2*sqrt(5)]/4



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micahwood50
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HINT: 180º/5 = 36º

tanjung
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next, what's formula using i do

micahwood50
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Seems like it won't help. Try this, using the formula sin (a + b) = cosa sinb + cosb sin a
sin36º = 2 sin18º cos18º = 2 cos72º sin72º

tanjung
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ok, i know that formula..
but i think we get the new problem... because sin/cos 18 or sin/cos 72 not eassy to get.. it's very difficul, right ?

micahwood50
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It seems so. Bump your question to get more helps. Maybe someone can help you with this.

tanjung
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ok, thanks...

tanjung
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@cwrw238 , @experimentX , @estudier , @Hero , @Zarkon , @sauravshakya , @all... help me please, how to get it

tanjung
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any idea guys ?

ajprincess
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dw:1350231015827:dwdw:1350231152168:dw
Use quadratic formula
dw:1350231253477:dw
dw:1350231349862:dw

experimentX
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@ajprincess try thisdw:1350231460480:dw

tanjung
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ok, i get
dw:1350231717622:dw

tanjung
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next ?

tanjung
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upss. sorry, divided 8

ajprincess
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dw:1350231971343:dwdw:1350232035700:dw

ajprincess
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@experimentX I tried bt it is a bit complex. cos sin3x=sin108.

ajprincess
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Getting it @tanjung?

experimentX
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this should be simpler ... sin(3x) = sin(2x)

tanjung
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not yet, what should i do after that

experimentX
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since this is just double angle and triple angle ... change everything back to sin ... and remove all roots and try to factorize it.

ajprincess
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dw:1350232254804:dw

tanjung
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so, just take positive sign in sqrt ?

tanjung
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i know that + it means there are two number here. what about u for it

mukushla
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with positive sign u have sin 36>1 thats impossible

ajprincess
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dw:1350233305717:dw

tanjung
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oh yea, i understand now...
thank u very much for ur help , @ajprincess and @mukushla

ajprincess
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yw:)