因为:a/(ab+a+1)=a/(ab+a+abc)=1/(b+1+bc)
可知: a/(ab+a+1)=1/b *b/(bc+b+1)
又有:c/(ca+c+1)=c/(ca+c+abc)=1/(a+1+ab)=1/a* a/(ab+a+1)
=1/a* 1/b *b/(bc+b+1)=1/ab* b/(bc+b+1)
所以:a/(ab+a+1) +b/(bc+b+1) +c/(ca+c+1)
=1/b *b/(bc+b+1)+b/(bc+b+1)+1/ab* b/(bc+b+1)
=(a+ab+abc)/(a+ab+abc)
=1