A I___________I
I-------------I-------------I---------------I
2xAB(dublul segmentului)= AB/3+3cm / impartire AB/3=treimea segmentului
2xAB=AB/3 +3
AB /3 +3=2 AB
AB/3+9 /3=2AB
AB+9=2AB x3
6AB -AB=9
5AB=9
AB=9 /5
verificare
2xAB=AB/3 +3
2x9/5 =9/5/3 +3
18 /5 =9/5/3+3
18/5 =9 /5x1/3 +3
18/5=9/15+3
18/5=3/5 +3
18/5=3/5+15/3
18/5=18/5