cos(-兀\6)+cos(兀-6)+cos(2兀-兀\6)+••+cos(2012兀-兀\6)求之

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cos(-兀\6)+cos(兀-6)+cos(2兀-兀\6)+••+cos(2012兀-兀\6)求之
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cos(-兀\6)+cos(兀-6)+cos(2兀-兀\6)+••+cos(2012兀-兀\6)求之
cos(-兀\6)+cos(兀-6)+cos(2兀-兀\6)+••+cos(2012兀-兀\6)求之

cos(-兀\6)+cos(兀-6)+cos(2兀-兀\6)+••+cos(2012兀-兀\6)求之
cos(-兀\6)+cos(兀-π/6)+cos(2兀-兀\6)+••+cos(2012兀-兀\6)
=cos(π/6)-cos(π/6)+cos(π/6)-.+cos(π/6)
=cos(π/6)
=1/2