cho tam giac abc can tai a ( a > 90 ) ve duong trung truc ab,ac cat canh nay o m,n va cat bc tai o,i a) tam giac aob,aic la tam giac gi
b) goi d la giao diem mo,ni , chung minh tam giac amd =and
c) chung minh d la truc tam cua 2 tam giac aob va aic
ve hinh day du ho minh nhe