已知1/a+1/b=1/6,1/b+1/c=1/9,1/a+1/c=1/15,求abc/(ab+bc+ac)的值

Answer 1

（ab+bc+ac)/abc=1/a+1/b+1/c=1/2(1/a+1/b+1/a+1/c+1/b+1/c)=1/2(1/6+1/9+1/15)=31/180,固原式=180/31