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Thread: Prove the equation without the calculator

  1. April 21st 2009, 03:00 AM #1
    beq!x
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    Prove the equation without the calculator

    Prove the equation without the calculator
    8cos20^\circ cos40^\circ cos80^\circ=1
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  2. April 21st 2009, 03:07 AM #2
    bebrave
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    8cos20.cos40.cos80
    =(8sin20.cos20.cos40.cos80)/(sin20)
    =(4sin40.cos40.cos80)/(sin20)
    =(2sin80.cos80)/(sin20)
    =2sin160/sin20=1
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  3. April 21st 2009, 02:15 PM #3
    beq!x
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    can you tell me please which formula have you used ?
    and i have a little bit trouble at the end " 2sin160/sin20=1" why?
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