{an}是等差数列,设公差是d 则a(n+1)=an+d 所以bn=2an+3an+3d=5an+3d 所以b(n-1)=5a(n-1)+3d bn-b(n-1)=5[an-a(n-1)]=5d是常数 所以bn也是等差数列
