an-1=2an+1/22an+1/2+1/2=2(an+1/2)=a(n-1)+1/2(an+1/2)/[a(n-1)+1/2]=1/2令bn=an+1/2,b1=a1+1/2=5/2数列{bn}是一个首项是5/2,公比是1/2的等差数列bn=5/2*(1/2)^(n-1)=5*(1/2)^nan=bn-1/2=5*(1/2)^n-1/2a2011=5*(1/2...