cho tam giac abc ; m la điêm tren canh bc sao cho bm = 2 cm . n la diem tren canh ac sao cho cn = 3 x na. am cat bn tai o . hay tinh dien tich tam giac abc , nếu biêt dien tich tam giac aob la 20cm2
AI LAM DUOC CHO 999999999999999999999999999999999999999999999999999999999999999K