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Cos20.cos40.cos60.cos80=1/16

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Cos20.cos40.cos60.cos80=1/16
  • 1 answers

Priya Singh 7 years, 4 months ago

=(1/8)cos80°+(1/8)cos100°+(1/8)cos60°
=(1/8)(cos80°+cos100°)+(1/8)×(1/2)
=(1/8)[{2cos(80°+100°)/2}{cos(80°-100°)/2}]+(1/16)
=(1/8)(2cos90°cos10°)+(1/16)
=0+(1/16) [cos90°=0]
=1/16 (proved)
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