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Prove that: ` cos ((2pi)/15) . cos ((4pi)/15) . cos ((8pi)/15) . cos ((16pi)/15) = 1/16` |
Answer» `cos2pi/15*cos4pi/15*cos8pi/15*cos(pi+pi/15)` `(2sinpi/15*cospi/15*cos2pi/15*cos4pi/15*cos8pi/15)/(2sinpi/15` `(-2sin2pi/15cos2pi/15*cos4pi/15*cos8pi/15)/(2*2sinpi/15)` `(-sin4pi/15cos4pi/15*cos8pi/15)/(24sinpi/15)` `(sinpi/15)/(16sinpi/15)=1/16` proved. |
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