2n*(2n+2)*(2n+4)*(2n+6)+16
=16n(n+1)(n+2)(n+3)+16
=16[n(n+1)(n+2)(n+3)+1]
=16[(n+1)(n+2)*n(n+3)+1]
=16[(n?+3n+2)(n?+3n)+1]
=16[(n?+3n)?+2(n?+3n)+1]
=16(n?+3n+1)?
a1=S1=-1
n≥2时
an=Sn-S(n-1)
=2n?-3n-2(n-1)?+3(n-1)
=4n-3
=4n-5
由于a1=-1也满足上式,因此an一定是等差数列
成立。
如果认为讲解不够清楚,请追问。
祝:学习进步!