一道数学题···麻烦各位高手··求证:cos(π/2k+1)-查字典问答网

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　　一道数学题···麻烦各位高手··求证:cos(π/2k+1)+cos(2π/2k+1)+…+cos(2k-1)π/2k+1+cos2kπ/2k+1=0

　　一道数学题···麻烦各位高手··

　　求证:cos(π/2k+1)+cos(2π/2k+1)+…+cos(2k-1)π/2k+1+cos2kπ/2k+1=0

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2020-03-0413:09

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齐家月

　　注意到cos(π-x)=-cos(x)所以左端首尾相加是0,所以2(cos(π/2k+1)+cos(2π/2k+1)+…+cos(2k-1)π/2k+1+cos2kπ/2k+1)=(cos(π/2k+1)+cos2kπ/2k+1)+(cos(2π/2k+1)+cos(2k-1)π/2k+1)...+(cos2kπ/2k+1+cos(π/2k+...

2020-03-04 13:13:17

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