bạn làm như sau (xloi nha mình moi giaa nhap nen kieu trinh bay hoi xau)
$x/(b+c)-a/(b+c)+x/(c+a)-b/(c+a)+x/(a+b)-c/a+b=3x/(a+b+c)$ $<=>x(1/(b+c)+1/(c+a)+1/(a+b)-3/(a+b+c))=a/(b+c)+b/(a+c)+c/(a+b)$
$<=>x(1/(b+c)-1/(a+b+c)+1/(a+c)-1/(a+b+c)+1/(a+b)-1/(a+b+c))=a/(b+c)+b/(a+c)+c/(a+b) $...