已知数列｛an｝是等差数列,Sn是前n项和若Sm=n Sn=m 求Sm+n

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已知数列｛an｝是等差数列,Sn是前n项和若Sm=nSn=m求Sm+n已知数列｛an｝是等差数列,Sn是前n项和若Sm=nSn=m求Sm+n已知数列｛an｝是等差数列,Sn是前n项和若Sm=nSn=m

已知数列｛an｝是等差数列,Sn是前n项和若Sm=n Sn=m 求Sm+n
已知数列｛an｝是等差数列,Sn是前n项和若Sm=n Sn=m 求Sm+n

已知数列｛an｝是等差数列,Sn是前n项和若Sm=n Sn=m 求Sm+n
Sm+n=0,设首项为a1,Sm=a1+(m-1)*d=n,Sn=a1+(n-1)*d=m,两式相减,易知(n-m)*d=m-n,得d=-1;
因而a1=m+n-1；Sm+n=a1+(m+n-1)*(-1)=0;

Sm=a1+(m-1)*d=n就错了am=a1+(m-1)*d=n

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已知数列｛an｝是等差数列,Sn是前n项和 若Sm=n Sn=m 求Sm+n

已知数列｛an｝是等差数列,Sn是前n项和若Sm=n Sn=m 求Sm+n