a/(ab+a+1)=a/(ab+a+abc)=1/(b+1+bc)c/(ac+c+1)=bc/(abc+bc+b)=bc/(1+bc+b)所以，a/(ab+a+1)+b/(bc+b+1)+c/(ac+c+1)=1/(bc+b+1)+b/(bc+b+1)+bc/(bc+b+1)=1
