an+1=10根号an,
lg(an+1)=lg10+1/2lgan
设bn=lgan
b(n+1)=1+1/2bn
b(n+1)-2=(1/2)(bn -2)
{bn -2}是等比数列,首项lg10 -2=-1,公比1/2
bn -2=-(1/2)^(n-1)
bn=2-(1/2)^(n-1)
an=10^[2-(1/2)^(n-1)]
an+1=10根号an,
lg(an+1)=lg10+1/2lgan
设bn=lgan
b(n+1)=1+1/2bn
b(n+1)-2=(1/2)(bn -2)
{bn -2}是等比数列,首项lg10 -2=-1,公比1/2
bn -2=-(1/2)^(n-1)
bn=2-(1/2)^(n-1)
an=10^[2-(1/2)^(n-1)]