已知数列AN的前N项和SN,SN=2N^2+3n+2,求an
4个回答
A(n+1)
=S(n+1)-Sn
=2(n+1)^2+3(n+1)+2-2n^2-3n-2
=2n^2+4n+2+3n+3-2n^2-3n
=4n+5
An=5+4(n-1)
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