Tu had
Cays Cho SABC roj tai A. Tren cans AC by drain D
von le attion (0) when co lam duong kins, bc cat (0)
tai C, B) cat (@) tai E; AE cat (0) tai F.
Ching as The grúc ABCE nostrep. b) & BCA = SACE
c) Lay Mitoxing Dqua A, Naňixing D quedthing Be
Chuns: BA+ BNC = 180°