等差数列an的前n项和为Sn,若a1=2,s3=12求an
1个回答
S3=a1+a2+a3=3(a1+a3)/2=12
a1+a3=8 a3=6
d=a3-a1 /2=2
an=a1+(n-1)d=2+2n-2=2n
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