{a;b} d.p. {2;9} inseamna sir de rapoarte egale.
[tex] \frac{a}{2} = \frac{b}{9} =k \\ a=2k \\ b=9k \\ a\cdotb=72 \\ 2k\cdot9k=72 \\ 18k^2=72 \\ k^2=4 \\ k=\pm2 \\ \hbox{Datorita proportionalitatii, se alege doar k=2.}\\ a=2k=4 \\ b=9k=18 \\ Verificare:\\ 4\cdot18=72 \\ \frac{4}{2}= \frac{18}{9} [/tex]
