f(x)f(x+2)= 3
得f(x+2)= 3/f(x)
f(1)=2
f(3)= 3/f(1)= 3/2
f(5)= 3/f(3)=2
f(7)= 3/f(5)= 3/2
.
所以
f(1)=f(5)=f(9)=...=2
f(3)=f(7)=f(11)=...= 3/2
所以
f(2011)=f(3+2008)=f(3+502×4)=f(3)= 3/2