等差数列{an}的前n项和记为Sn.以已知a10=30,a20=50.令bn=2^(an-10),求数列{bn}的前n项和Tn

A20-A10=50-30=20=10dd=2A1=A10-9d=30-18=12An=A1+(n-1)d=12+2(n-1)=2n+10(An)-10=2nBn=2^(An-10)=2^(2n)=4^n{Bn}是等比数列Tn=B1×(1-q^n)/(1-q)=4×(1-4^n)/(1-4)=(4/3)×(4^n-1)