由F(-∞,y)=0,得A(B-π/2)(C+arctany/3)=0,B=π/2.
由F(x,-∞)=0,得A(B+arctanx/2)(C-π/2)=0,C=π/2.
由F(+∞,+∞)=1,得A(B+π/2)(C+π/2)=1,A=1/π^2.