Notam trapezul ABCD
AB=6
DC=4
ducem linia mijlocie MN care intersecteaza AC in E si DB in F
ME linie mijlocie in triunghiul ADC ME=DC/2=4/2=2
FN linie mijlocie in triunghiul BDC FN=DC/2=4/2=2
MN linie mijlocie in trapez =(4+6)/2=5
EF=5-2-2=1
sau direct
EF=(AB-DC)/2=(6-4)/2=2/2=1
ME=EF=4/2=2