<br>1、n为奇数:<br>S奇-S偶=(2a1+nd)/2;S奇/S偶=(n+1)/(n-1),<br>因为:S奇=(a1+an)*|n/2|/2=(a1+(a1+nd))*(n+1)/4 = (2a1+nd)*(n+1)/4<br>S偶=(a2+An-1)*|n/2|/2=((a1+d)+(a1+(n-1)d))*(n-1)/4 = (2a1+nd)*(n-1)/4<br>2、n为偶数:<br>则 S奇=(a1+An-1)*|n/2|/2=(a1+a1+(n-1)d)*n/4 = (2a1+nd-d)*n/4<br>S偶=(a2+An)*|n/2|/2=(a1+d+a1+nd)*n/2/2 = (2a1+nd+d)*n/4<br>所以 S奇-S偶=-2d*n/4=-dn/2;S奇/S偶=(2a1+nd-d)/(2a1+nd+d)
题目<br><img><br>答案解析<br>查看更多优质解析<br>举报<br>前N项和公式:Sn=na1+n(n-1)d/2<br>通项公式:an=a1+(n-1)d<br>解析看不懂?免费查看同类题视频解析<br>查看解答