证明:[1/(ab+a+1)]+[1/(bc+b+1)]+[1/(ac+c+1)]
=[1/(ab+a+abc)]+[1/(bc+b+1)]+[1/(ac+c+abc)]
=[1/a(b+1+bc)]+[1/(b+1+bc)]+[1/c(a+1+ab)]
=[1/a(b+1+bc)]+[1/(b+1+bc)]+[1/ac(b+1+bc)]
=1/(b+1+bc)*[(1/a)+1+(1/ac)]
=1/(b+1+bc)*[bc+1+b]
=1
证明:[1/(ab+a+1)]+[1/(bc+b+1)]+[1/(ac+c+1)]
=[1/(ab+a+abc)]+[1/(bc+b+1)]+[1/(ac+c+abc)]
=[1/a(b+1+bc)]+[1/(b+1+bc)]+[1/c(a+1+ab)]
=[1/a(b+1+bc)]+[1/(b+1+bc)]+[1/ac(b+1+bc)]
=1/(b+1+bc)*[(1/a)+1+(1/ac)]
=1/(b+1+bc)*[bc+1+b]
=1