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

Mathematics
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HINT: 180º/5 = 36º
next, what's formula using i do
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

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Other answers:

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 ?
It seems so. Bump your question to get more helps. Maybe someone can help you with this.
ok, thanks...
@cwrw238 , @experimentX , @estudier , @Hero , @Zarkon , @sauravshakya , @all... help me please, how to get it
any idea guys ?
|dw:1350231015827:dw||dw:1350231152168:dw| Use quadratic formula |dw:1350231253477:dw| |dw:1350231349862:dw|
@ajprincess try this|dw:1350231460480:dw|
ok, i get |dw:1350231717622:dw|
next ?
upss. sorry, divided 8
|dw:1350231971343:dw||dw:1350232035700:dw|
@experimentX I tried bt it is a bit complex. cos sin3x=sin108.
Getting it @tanjung?
this should be simpler ... sin(3x) = sin(2x)
not yet, what should i do after that
since this is just double angle and triple angle ... change everything back to sin ... and remove all roots and try to factorize it.
|dw:1350232254804:dw|
so, just take positive sign in sqrt ?
i know that +- it means there are two number here. what about u for it
with positive sign u have sin 36>1 thats impossible
|dw:1350233305717:dw|
oh yea, i understand now... thank u very much for ur help , @ajprincess and @mukushla
yw:)

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