Răspuns:
/- supra
ab+bc+ca/ac+cb+ba=
=10a+b+10b+c+10c+a/10a+c+10c+b+10b+a=
=11a+11b+11c/11a+11b+11c=
=11×(a+b+c)/11×(a+b+c)= simplificăm prin 11
=1×(a+b+c)/1×(a+b+c)=
=a+b+c/a+b+c
