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Cho goc xAC= 110 do, goc CBy=50 do, AC
B=120 do, cm Ax// By
goc XAO = 110 do
goc YBO = 120 do
va OA vuong goc OB
chung minh AX // BY
trong hinh ben cho biet goc xAB= a do; goc ABC = a do + b do ; CBy=108 do - b do. Ax vuong goc voi m; Cz vuong goc voi n
Cho tam giac ABC co: goc B=70 do, goc C=50 do. LAy M thuoc AB sao cho goc ABM=20 do; lay N thuoc AB sao cho goc ACN= 10 do. P la giao diem cua BM va CN. Chung minh rang: MN=2PM.
cho goc xOy = 110 do va tia Oz la tia phan giac cua goc do. tren tia Ox lay diem M, dung tia Mt nam trong goc do sao cho OMt = 70 do
a, chung minh Mt \\ Oy
b, goi Mt' la tia doi cua Mt, Mn la tia phan giac cua goc OMt'. chung minh Mn \\Oz
cho goc BAx co so do bang 70 .tu B ke duong thang By song song Ax,BC vuong goc voi . so do goc CDB
cho doan thang AB.Tren cung 1 nua mat phang bo AB ve 2 tia Ax va By trong do goc BAx = an-pha va goc ABy=4.an-pha.tinh an-pha de cho Ax song song voi By
cho tam giac ABC can tai A , goc A = 110 do. tren canh BC lay diem D sao cho goc CAD = 70 do. ke tia Cx song song voi AD cat tia BA tai E . chung minh tam giac AEC can
cho tam giac ABC co goc ABC=100 do . D la diem tren tia doi cua tia BC. ve tia Dx sao cho cac goc BDx va goc ABDA so le trong va goc BDX = 80 do . Chung minh rang : AB//Dx