λ=1/2,下面是理由
设an-μ=3(a(n-1)-μ) 3^n移项得an=3a(n-1) 3^n-2μ,即μ=-1/2
故an 1/2=3(a(n-1) 1/2) 3^n
等式两边同时除以3^n,可得
(an 1/2)/3^n=(a(n-1) 1/2)/3^(n-1) 1
所以数列{(an 1/2)/3^n}为等差数列,公差为1