Question

已知数列An是各项均为正数的等差数列,lga1,lga2,lga4成等差数列,又Bn=1/A(2^n),n=1,2,3,

Answer 1

因为lga1,lga2,lga4成等差数列lga1+lga4=2lga2,lga1*a4=lg（a2）^2所以a1*a4=（a2）^2a1(a1+3d)=(a1+d)^2得a1=dan=ndBn=1/d2^n B（n-1）=1/d2^(n-1) B（n+1）=1/d2^(n+1)B（n-1） B（n+1）=1/d2^(n-1)*=1/d2^(n+1)=(...