E=1/2AB
D=1/2AC
ED-linia mijlocie a triunghiului
ED II BC
EB=DC
m unghiurilor alaturate bazei unui triunghi isoscel sunt congruente deci :
m∠A=m∠B+m∠C=180°
m∠B=m∠C=(180-m∠A)/2=70°
m∠D+m∠E+m∠B+m∠C=360°
m∠D=m∠E=(360-70*2)/2=110°
m∠D=m∠E=110°
m∠C=m∠B=70°
