已知数列{an}为等差数列,若a1=-3,11a5=5a8,则使前n项和Sn取最小值的n=________.
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已知数列{an}为等差数列,若a1=-3,11a5=5a8,则使前n项和Sn取最小值的n=________. |
答案
2 |
解析
∵a1=-3,11a5=5a8,∴d=2,∴Sn=n2-4n=(n-2)2-4,∴当n=2时,Sn最小. |
举一反三
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