a 1= 1,q=2
an=a 1q? = 1 2? =2?
bn=3+log2(an)
=3+log2(2? )
=3+(n- 1)
=n+2
b 1= 1+2=3
B (n+1)-bn = [(n+1)+2]-(n+2) =1,which is a fixed value.
Sequence {bn} is a arithmetic progression, the first term is 3, and the tolerance is 1.