Dung DH vuong goc vs AB suy ra BH=HA=CD=12AD=>^HDA=30oGoi giao cua AD va BC la E. Suy ra D la Trung diem cua AE va ^BEA=^HDA=30o
Lap pt duong thang AD di qua N(-2,0) va tao vs BC goc 30o
Tu pt AD lap dk tim ra E.
Tim dk E ta tim dk D thong qua →ED=23→EM
Tim dk D se lap dk pt duong DC qua D vuong BC.
Giao cua DC tim dk va BC ta tim dk C.