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
问题描述：
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
答
（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