cho tam giac abc,ab<ac,phan giac ad.Tren canh ac lay diem e sao cho ab=ae.Tia eb cat ab tai diem k. 1cm:bd=de va da la phan giac cua goc bde 2.cm:goc kbd=goc crd va goc dkc=goc dck 3.cm;tam giac akc can va ad vg goc kc