1.数列{an}中,an=an-1+1/2(n>=2,n属于N*),an=3/2,前n项和Sn=-15/2,则a1=___,n=___.2.已知数列的Sn=n²+n+1,则a8+a9+a10+a11+a12=_____.

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1.数列{an}中,an=an-1+1/2(n>=2,n属于N*),an=3/2,前n项和Sn=-15/2,则a1=___,n=___.2.已知数列的Sn=n²+n+1,则a8+a9+a10+a11+a12=_____.
1.数列{an}中,an=an-1+1/2(n>=2,n属于N*),an=3/2,前n项和Sn=-15/2,则a1=___,n=___.
2.已知数列的Sn=n²+n+1,则a8+a9+a10+a11+a12=_____.

1.数列{an}中,an=an-1+1/2(n>=2,n属于N*),an=3/2,前n项和Sn=-15/2,则a1=___,n=___.2.已知数列的Sn=n²+n+1,则a8+a9+a10+a11+a12=_____.
(1)数列{an}是公差为1/2的等差数列,an=a1+(n-1)d=3/2,
Sn=-15/2,联立解得a1=-3,n=10.
(2)由Sn=n^2+n+1,得,an=Sn-Sn-1=n^2+n+1-[(n-1)^2+(n-1)+1]=2n
于是a8+a9+a10+a11+a12=2(8+9+10+11+12)=100