1/ goc AMB =CME doi dinh
tam giac ABM = ECM (c-g-c)
b/ goc BAM = MEC
tu giac ABEC la hinh binh hanh (2 dg cheo cat nhau tai trung dienmmoi dg)
=> AB =EC
ma AC >AB (AC la canh huyen trong tam giac vg)
=> AC > EC
trong tam giac AEC ta co AC >EC ; goc doi dien voi canh nao lon hin thi lon hon
=>goc MEC > MAC
hay goc BAM > MAC
c/ co ngay BE //AC vi tu giac ABEC la hinh binh hanh theo t/c hbh
d/ lai co BA //EC (tinh chat hinh binh hanh)
BC vuong goc voi AC ( ABC =90)
=> EC vuong goc voi BC
2/
tam giac ABC can thi goc ABC =ACB
=> HBD = KCE (doi dinh)
xet 2 tam gic HBD vs KCE la 2 tam giac vuong co canh huyen bang nhau
2 goc nhon bang nhau
=> tam giac HBD = KCE ( canh huyen - goc nhon)
=> HB = CK ( 2 canh tuonh\g ung )
b/
tam giac ABH =ACK ( c-g-c)
( AB =AC ; HB =CK ; goc HBA =KCA vi cung bu voi 2 goc bang nhau)
= > goc AHB = AKC( 2 goc tuong ung)
c/
ti so AB / BD = AC /CE (AB =AC ; BD = CE)
theo dinh ly dao dinh ly talet thi BC//DE
hay HK // DE
