设等差数列{an}的前n项和为Sn,且a3+a7-a10=8,a11-a4=4,则S13等于?方法通俗易懂最好,本人基础不好
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![设等差数列{an}的前n项和为Sn,且a3+a7-a10=8,a11-a4=4,则S13等于?方法通俗易懂最好,本人基础不好](/uploads/image/z/3022442-26-2.jpg?t=%E8%AE%BE%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%7Ban%7D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn%2C%E4%B8%94a3%2Ba7-a10%3D8%2Ca11-a4%3D4%2C%E5%88%99S13%E7%AD%89%E4%BA%8E%3F%E6%96%B9%E6%B3%95%E9%80%9A%E4%BF%97%E6%98%93%E6%87%82%E6%9C%80%E5%A5%BD%2C%E6%9C%AC%E4%BA%BA%E5%9F%BA%E7%A1%80%E4%B8%8D%E5%A5%BD)
设等差数列{an}的前n项和为Sn,且a3+a7-a10=8,a11-a4=4,则S13等于?方法通俗易懂最好,本人基础不好
设等差数列{an}的前n项和为Sn,且a3+a7-a10=8,a11-a4=4,则S13等于?
方法通俗易懂最好,本人基础不好
设等差数列{an}的前n项和为Sn,且a3+a7-a10=8,a11-a4=4,则S13等于?方法通俗易懂最好,本人基础不好
很高兴能为您解答.
等差数列通项公式an=a1+(n-1)d
a3+a7-a10=a1+2d+a1+6d-a1-9d=8,1式
a11-a4= a1+10-a1-3d= 4 ,2式
化简得
a1-d=8
7d=4
则,a1=60/7,d=4/7
等差数列前n项和公式为
sn=na1+{n(n-1)}/2
s13=13*(60/7)+{(13*12)/2}*4/7=156
加油!
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