Prove the equation without the calculator $\displaystyle 8cos20^\circ cos40^\circ cos80^\circ=1$
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8cos20.cos40.cos80 =(8sin20.cos20.cos40.cos80)/(sin20) =(4sin40.cos40.cos80)/(sin20) =(2sin80.cos80)/(sin20) =2sin160/sin20=1
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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