cho goc xoy bang 60 fo .qua A tren Ox ve Az sao cho OAz bang 120 do .qua B trenAz ke duong thang MN cat Oy tai C sao cho MBz bang 60 do .ke OH vuong goc voi Oy tai K;C la giao diem cua MN va Oy

a, chung minh Az song song voi OY

b. c/m Ox song song voi mn

c.tinh OBC

d. c/m OH song song DK

cho bz - cy/a= cx-az/b=ay-bx/c

chung minh rang x/a = y/b = z/c

giai nhan ho mik vs mik can gap

cho tam giac ABC .M la trung diem cua BC .goi H,K lan luot la hinh chieu cua B,C tren AM chung minh tu giac BHCK la hinh binh hanh .Tu do suy ra CH song song vs BK