2n+1项的总和=(A1+A(2n+1))*(2n+1)/2=(A1+nd)*(2n+1)
偶数项,共有N项,且首项为A1,公差为2d,求和得=(A1+nd)*n
则奇数项的和=(A1+nd)*(2n+1)-(A1+nd)*n=(A1+nd)*(n+1)
则奇数项和:偶数项和=(n+1)/n
2n+1项的总和=(A1+A(2n+1))*(2n+1)/2=(A1+nd)*(2n+1)
偶数项,共有N项,且首项为A1,公差为2d,求和得=(A1+nd)*n
则奇数项的和=(A1+nd)*(2n+1)-(A1+nd)*n=(A1+nd)*(n+1)
则奇数项和:偶数项和=(n+1)/n