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1、n为奇数:
S奇-S偶=(2a1+nd)/2;S奇/S偶=(n+1)/(n-1),
因为:S奇=(a1+an)*|n/2|/2=(a1+(a1+nd))*(n+1)/4 = (2a1+nd)*(n+1)/4
S偶=(a2+An-1)*|n/2|/2=((a1+d)+(a1+(n-1)d))*(n-1)/4 = (2a1+nd)*(n-1)/4
2、n为偶数:
则 S奇=(a1+An-1)*|n/2|/2=(a1+a1+(n-1)d)*n/4 = (2a1+nd-d)*n/4
S偶=(a2+An)*|n/2|/2=(a1+d+a1+nd)*n/2/2 = (2a1+nd+d)*n/4
所以 S奇-S偶=-2d*n/4=-dn/2;S奇/S偶=(2a1+nd-d)/(2a1+nd+d)