se duce MF IIAB
rezulta ca MF linie mijlocie in triunghiul ADP
FM=AB=14 cm
FM=DP/2
DP=2FM=2*14=28 cm
triunghiurile ANB si DNP sunt asemenea (au unghiuri congruente)
m(<NDP)=m(<ABN)
m(<NPD)=m(<NAB)
m(<DNP)=m(<ANB)
putem scrie AB/DP=NB/DN
14/28=NB/(18-NB)
1/2=NB/(18-NB)
2NB=18-NB
3NB=18
NB=18/3=6 cm