`(x-ab)/(a+b)+(x-ac)/(a+c)+(x-bc)/(b+c)=a+b+c`
`<=>(x-ab)/(a+b)+(x-ac)/(a+c)+(x-bc)/(b+c)-a-b-c=0`
`<=>((x-ab)/(a+b)-c)+((x-ac)/(a+c)-b)+((x-bc)/(b+c)-a)=0`
`<=>(x-ab-ac-bc)/(a+b)+(x-ac-ab-bc)/(a+c)+(x-bc-ab-ac)/(b+c)=0`
`<=>(x-ab-ac-bc)(1/(a+b)+1/(a+c)+1/(b+c))=0`
`text(Xét 2 TH`
`TH1:1/(a+b)+1/(a+c)+1/(b+c)=0`
`tox-ab-ac-bcne0`
`to text(vô nghiệm)`
`TH2:1/(a+b)+1/(a+c)+1/(b+c)ne0`
`tox-ab-ac-bc=0`
`tox=ab+ac+bc`
