过程有些烦哦
令bn=an+kn+b
b(n+1)=a(n+1)+k(n+1)+b
又b(n+1)=2bn
a(n+1)+k(n+1)+b=2an+2kn+2b
a(n+1)=2an+kn+b-k=2an+2n-3
k=2 b=-1
bn=an+2n-1=3*2^(n-1)
an=3*2^(n-1)-2n+1