∠CAB=∠ADB, ∠ACB=∠DAB都是根据弦切角定理.
然后得到△ABC ∽ △DBA (AA).
则AC:DA = AB:DB, 即AC·BD = AD·AB.
另外∠ABC = ∠DBA = 180°-∠EBA.
弦AE与AC所对的圆周角互补, 可得AE = AC.
∠CAB=∠ADB, ∠ACB=∠DAB都是根据弦切角定理.
然后得到△ABC ∽ △DBA (AA).
则AC:DA = AB:DB, 即AC·BD = AD·AB.
另外∠ABC = ∠DBA = 180°-∠EBA.
弦AE与AC所对的圆周角互补, 可得AE = AC.