(1)sn-1=2an-1-3(n-1)
sn-sn-1=an=2(an-an-1)-3
an=2an-1+3
an+3=2(an-1+3)
an+3成等比数列 公比为2
当n=1时s1=a1=2a1-3
a1=3 即a1+3=6
an+3=6*2^n-1=3*2^n
an=3*2^n-3
(2)sn=2an-3n=6*2^n-6-3n
(1)sn-1=2an-1-3(n-1)
sn-sn-1=an=2(an-an-1)-3
an=2an-1+3
an+3=2(an-1+3)
an+3成等比数列 公比为2
当n=1时s1=a1=2a1-3
a1=3 即a1+3=6
an+3=6*2^n-1=3*2^n
an=3*2^n-3
(2)sn=2an-3n=6*2^n-6-3n