f(-1)=1/2
f(0)=1/2+√{f(-1)-[f(-1)]^2}=1
f(1)=1/2+√{f(0)-[f(0)]^2}=1/2
f(2)=1/2+√{f(1)-[f(1)]^2}=1
循环开始
n为正整数
f(2n)=1
f(2n+1)=1/2
f( 2009)=1/2
选A
f(-1)=1/2
f(0)=1/2+√{f(-1)-[f(-1)]^2}=1
f(1)=1/2+√{f(0)-[f(0)]^2}=1/2
f(2)=1/2+√{f(1)-[f(1)]^2}=1
循环开始
n为正整数
f(2n)=1
f(2n+1)=1/2
f( 2009)=1/2
选A