在等差数列{an}中,设前m项和为Sm,前n项和为Sn,且Sm=Sn,m不等于n,则Sm+n=?

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Sm=Snma1+m(m-1)d/2=na1+n(n-1)d/2
(m-n)a1+(m²-m-n²+n)d/2=0
(m-n)a1+[(m+n)(m-n)-(m-n)]d/2=0
a1(m-n)+d(m-n)(m+n-1)/2=0
a1+d(m+n-1)/2=0
a1=-d(m+n-1)/2
S(m+n)=(m+n)a1+(m+n)(m+n-1)d/2
=-(m+n)(m+n-1)d/2+(m+n)(m+n-1)d/2
=0