f (x )=l g (2+x )+l g (2-x ) =lg(4-x^2)
零和负数无对数,4-x^2>0,定义域-2<x<2
又:4-x^2≥4
∴0<4-x^2≤4
∴-∞ < lg(4-x^2) ≤ 2lg2
值域(-∞,2lg2]