等差数列{an}前n项和为sn,公差为d=3),使得am=sm,则当n>m(n∈N*)时sn和an(填,=)
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等差数列{an}前n项和为sn,公差为d=3),使得am=sm,则当n>m(n∈N*)时sn和an(填,=)
等差数列{an}前n项和为sn,公差为d=3),使得am=sm,则当n>m(n∈N*)时sn和an(填,=)
等差数列{an}前n项和为sn,公差为d=3),使得am=sm,则当n>m(n∈N*)时sn和an(填,=)
用图像最好做!应该是 <
用代数方法是这样的:an=a1+(n-1)d
Sn=a1+[n(n-1)d]/2
作差得:Sn-an=(n/2-1)(n-1)d
由题知,n>m>=3 ,d<0 所以Sn-an<0
即Sn
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