例2设f(x)=1(x+x) x。x<0 ,求g(x),Sx) x2≥0 解:g()=g(x)+g(x) (x-x)=0,x<0 (x2+x2)=x2,x≥0     = = + , 0 , 0 ( ) ( ) 2 1 ( ) 2 x x x x g x 例2 设 f x x x ,求f[g(x)], g[f(x)] 解: f[g(x)]= [ ( ) ( )] 2 1 g x + g x = ( ) , x<0 2 1 x − x =0 ( ) , x≥0 2 1 2 2 x + x =x 2