有两个各项an,bn都是正数的数列和,如果a1=1,b1=2,a2=3,且an,bn,an+1成等差数列,bn,an+1

an+an+1=2*bn
bn+bn+1=2*an+1
2*bn+2*bn+1=4*an+1
an+an+1+an+1+an+2=4*an+1
an+an+2=2*an+1等差
an=2n-1
bn=2n