S3=a7,所以3a1+3d=a1+6d,即2a1=3d,a8-2a3=3d-a1=a1=3,所以d=2,那么an=a1+(n-1)d=2n+1.
设Sn为等差数列{An}的前n项和,已知S3=a7,a8-2a3=3 求an等于多少
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