作业帮{an}是等差数列,前n项和为Sn,且S2011/2011-S2009/2009=1,则公差d为?
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{an}是等差数列,前n项和为Sn,且S2011/2011-S2009/2009=1,则公差d为?
{an}是等差数列,前n项和为Sn,且S2011/2011-S2009/2009=1,则公差d为?
{an}是等差数列,前n项和为Sn,且S2011/2011-S2009/2009=1,则公差d为?
S2011/2011=(a1+a2011)/2
S2009/2009=(a1+a2009)/2
S2011/2011-S2009/2009
=(a1+a2011)/2-(a1+a2009)/2
=1/2(a2011-a2009)
=1/2 x 2d=d
∴d=1
1