解(1 F(+∞,+∞)=AB+ 兀C+ F(-∞,+∞)=AB F(+0,-0)=AB 2π2π2三 C+x=0 兀\=0 丌 B C=-A 2 (2)Fx(x)=F(x,+∞) t-arctan 0<x<+0解 (1) 1 2 2 ( , )  =       +      + + = +   F A B C 0 2 2 ( , )  =       +      − + = −   F A B C 0 2 2 ( , )  =       −      + − = +   F A B C 2 1 , 2 , 2    B = C = A = (2) F (x) = F(x,+) X , , 2 arctan 1 2 1 = + −   x  + x 