Ta có:
DBDC=DBDC= ABAC=ABAC= 2323 ⇔ DB=2/3DC
MàDB+DC=7,5⇒2/3DC+DC=7,5⇔5/3DC=7,5⇔DC=4,5DB+DC=7,5⇒2/3DC+DC=7,5⇔5/3DC=7,5⇔DC=4,5⇒DB=3DB=3
EBEC=EBEC= ABAC=ABAC= 2323 ⇔EB=2/3EC
MàEC−EB=7,5⇒EC−2/3EC=7,5⇔EC/3=7,5⇔EC=22,5EC−EB=7,5⇒EC−2/3EC=7,5⇔EC/3=7,5⇔EC=22,5⇒BE=15
ED=EB+BD=15+3=18
Vậy : DC=4,5 cm ; BE=15cm ; ED=18cm