cos5分之2派为什么等于-cos5分之3派

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cos5分之2派为什么等于-cos5分之3派

cos5分之2派为什么等于-cos5分之3派
cos5分之2派为什么等于-cos5分之3派

cos5分之2派为什么等于-cos5分之3派
诱导公式

(1)cos(π/5)+cos(2π/5)+cos(3π/5)+cos(4π/5)
  =cos(π/5)+cos(2π/5)-cos(2π/5)-cos(π/5)
  =0
(2)tan10°+tan170°+sin1866°-sin(-606°)
  =tan10°+tan(180°-10°)+sin(5*360°+66°)-sin(-360°-246°)

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(1)cos(π/5)+cos(2π/5)+cos(3π/5)+cos(4π/5)
  =cos(π/5)+cos(2π/5)-cos(2π/5)-cos(π/5)
  =0
(2)tan10°+tan170°+sin1866°-sin(-606°)
  =tan10°+tan(180°-10°)+sin(5*360°+66°)-sin(-360°-246°)
  =tan10°-tan10°+sin66°+sin246°
  =sin66°+sin(180°+66°)
  =sin66°-sin66°
  =0

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