等差数列an中,若3n²+2n,则公差d=
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等差数列an中,若3n²+2n,则公差d=
![等差数列an中,若3n²+2n,则公差d=](/uploads/image/z/7112691-27-1.jpg?t=%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97an%E4%B8%AD%2C%E8%8B%A53n%26sup2%3B%2B2n%2C%E5%88%99%E5%85%AC%E5%B7%AEd%3D)
Sn=3n^2+2n
S(n-1)=3(n-1)^2+2(n-1)
=3n^2-6n+3+2n-2
=3n^2-4n+1
an=Sn-S(n-1)
=3n^2+3n-(3n^2-4n+1)
=3n^2+3n-3n^2+4n-1
=7n-1
d=7
S(n-1)=3(n-1)^2+2(n-1)
=3n^2-6n+3+2n-2
=3n^2-4n+1
an=Sn-S(n-1)
=3n^2+3n-(3n^2-4n+1)
=3n^2+3n-3n^2+4n-1
=7n-1
d=7
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