计算cos5分之派+cos5分之2派+cos5分之3派+cos5分之4派

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计算cos5分之派+cos5分之2派+cos5分之3派+cos5分之4派
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计算cos5分之派+cos5分之2派+cos5分之3派+cos5分之4派
计算cos5分之派+cos5分之2派+cos5分之3派+cos5分之4派

计算cos5分之派+cos5分之2派+cos5分之3派+cos5分之4派
因为 cos(π/5)=cos(π-4π/5)= -cos(4π/5)
同理 cos(2π/5)=cos(π-3π/5)= -cos(3π/5)
所以 cos(π/5)+cos(2π/5)+cos(3π/5)+cos(4π/5)
= -cos(4π/5)-cos(3π/5)+cos(3π/5)+cos(4π/5)
=0