Cho 1 duong thang cat 2 duong thang song song,Hay chung minh rang:

a,Cac tia phan giac cua 1 cap goc so le (hoac so le ngoai thi song song voi nhau

b,Cac tia phan giac cua 1 cap goc dong vi thi song song voi nhau.

c,Cac tia phan giac cua 1 cap goc trong cung phia(hoac ngoai cung phia) thi vuong goc voi nhau.

Chung to rang neu hai duong thang song song thi cac tia phan giac cua moi cap goc dong vi song song voi nhau.

cho 2 duong thang song song a và b và 1 cat tuyên c .hai tia phan giac cua 1 cap goc trong cung phai cat nhau tai i .chung minh rang i cach đều 3 dg thang a,b,c

|x-1,25|=2,75

Cho tam giac ABC co B=45°,C=75°. Phan giac BAC cat  canh BC tai M. Qua M ke dg thang song song voi dg thang AB cat canh AC tai N.

1, tinh so do cac goc BAC va goc AMB

2,tinh so do cac goc cua tam giac AMN

A=1/4/23-5/21-4/23+1,5+1/16/12

Cho tam giac ABC co B=45°,C=75°.phan giac BAC cat canh BC tai M. Qua M ke dg thang song song voi dg thang AB cat canh AC tai N

1, tinh so do goc BAC va goc AMB

2, tinh so do cac goc cua tam giac AMN

Ve hinh dum nha

cho hinh thang ABCD BC song song voi AD, phan giac goc A cat BC tai E, phan giac goc B cat AE tai F.

a. Chung minh AE vuong goc voi BF, AF =FE

b. M la trung diem AB. Dg thang MF cat CD tai N. Chung minh N la trung diem CD

tam giac ABC co tia phan giac cua goc B cat AC o D.Qua A ke duong thang song song voi BD,duong thang nay cat duong thang BC o E.Chung minh rang goc BEA = goc BAE

ghi gt kl cua cac dinh li sau , ve hinh 

a, neu 2 dg thang phan biet // dg thang thu 3 thi chung // voi nhau 

b, neu 2 tia phan giac cua 2 goc ke bu thi vuong foc voi nhau

can gap ngay bay gio

Cho biet tu diem A thuoc tia phan giac cua goc xoy co mu nha! ve duong thang song song voi Ox cat Oy tai B va ve duong thang song song voi Oy tai C a)chung minh BOA=AOC ,b) chung minh AO la tia phan giac cua BAC