Выражение 1/(1+a+ab)+1/(1+b+bc)+1/(1+c+ca)

1/(1+a+ab)+1/(1+b+bc)+1/(1+c+ca)=1+1/a+1/b+1/ab+1+1/b+1/bc+1+1/c+1/ca=3+((b+a+1+a)/ab)+((1+b)/bc)+((a+1)/ac)=3+((cb+2a+1)/cab)+((a+b)/cab)+((ba+1)/cab)=3+((cb+2a+1+a+b+ba+1)/bac=3+((3bc+4a+2)/bac)