值域1到正无穷 (1,+∞)
(1/9)^x=(1/3)^2x
y=(1/3)^2x+(1/3)^x+1,令t=(1/3)^x 则t>0
Y=t^2+t+1=（t+1/2)^2+3/4
对称轴是t=-1/2,则在t>0的范围里,y下限为t=0是y=1,最大为正无穷 (1,+∞)