ab/(a+b)=1/3 可得(a+b)/ab=3 ,a/ab+b/ab=3, 1/a+1/b=3……一式bc/(b+c)=1/4
(b+c)/bc= 4,b/bc+c/bc=4,1/b+1/c=4……二式ac/(a+c)=1/5
(a+c)/ac=5,a/ac+c/ac=5,1/a+1/c=5……三式二式-一式，1/b+1/c-(1/a+1/b)=4-3, 1/b+1/c-1/a-1/b=1,1/c-1/a=1……四式三式+四式，1/a+1/c+1/c-1/a=5+1,2x1/c=6,1/c=3,c=1/3将1/c=3分别代入三式和二式，可得1/a+3=5,1/a=2...
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