Unikey co van de, xin phep go ko dau
Thay O td AB
Can CM: O td EF
=> CM: AFBE la hinh binh hanh
=> CM: AF//BC (tuong tu => AE//BF)
=> CM: AFD=CBD
Vi D thuoc (O), AB duong kinh
=> ADB=90
ma AHF=90
=> ADFH la tgnt
=> AFD=AHD
*Chung minh HA phan giac CHD (bai nay kha pho bien nen hy vong ban tu chung minh
![Big Grin :D :D](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
)
=> AFD=1/2 CHD
Lai co CHOD noi tiep (de dang chung minh)
=> AFD=1/2 COD
=> AFD=CBD (goc noi tiep)
=> dpcm....