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Prove that cos(2pi)/(15)cos(4pi)/(15)cos...

Prove that `cos(2pi)/(15)cos(4pi)/(15)cos(8pi)/(15)cos(14pi)/(15)=1/(16)`

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`cos 2π/15 cos 4π/15 cos 8π/15 cos 16π/15`

`= cos(2π/15) cos(4π/15) cos(8π/15) cos(π + π/15)`

`= cos(2π/15) cos(4π/15) cos(8π/15) [-cos(π/15)]`

`= -[cos(4π/15) cos(π/15)] [cos(8π/15) cos(2π/15)]`

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