已知a+b|ab=3|1,b+c|ac=4|1,急

倒过来,就有
(a+b)/ab=3,1/a+1/b=3----(1)
(b+c)/bc=4,1/b+1/c=4----(2)
(a+c)/ac=5,1/a+1/c=5----(3)
(1)+(2)+(3),2/a+2/b+2/c=12,1/a+1/b+1/c=6----(4)
(4)-(1),1/c=3,c=1/3
(4)-(2),1/a=2,a=1/2
(4)-(3),1/b=1,b=1
再问： 1/a+1/b=3 1/b+1/c=4 1/a+1/c=5-是什么意思
再答： 把原来的分数倒过来，ab/(a+b)=1/3, (a+b)/ab=3, a/ab+b/ab=3, 1/b+1/a=3, 1/a+1/b=3,