a)m(∡ABC)=60°(din,ip,180°-90°-30°)
Daca,ΔDBC,echilat=>m(∡DBC)=60°
Daca,ΔEBA,echilat=>m(∡EBA)=60°
=>m(∡EBD)=60°+60°+60°=180°=>punctele,E,B,D,sunt,colineare
b)m(∡ACB)=30°(ip.)
m(∡BCD)=60°(ip.,ΔBCD,echilat.)
=>m(∡ACD)=90°=>AC_l_CD
c)Scuze...nu-mi,vine,nici,o,idee...