6)
m//n nên ta có:
\(\widehat{N_2}=\widehat{M_2}=120^o\) (đồng vị)
\(\widehat{M_3}=180^o-\widehat{M_2}=180^o-120^o=60^o\) (kề bù)
\(\widehat{M_1}=\widehat{M_3}=60^o\) (đối đỉnh)
\(\widehat{N_3}=\widehat{M_3}=60^o\) (đồng vị)
\(\widehat{M_4}=\widehat{M_2}=120^o\) (đối đỉnh)
\(\widehat{N_4}=\widehat{M_4}=120^o\) (đồng vị)
\(\widehat{N_1}=\widehat{M_1}=60^o\) (đồng vị)
Bài 7:
a//b
=>\(\widehat{ACD}+\widehat{BAC}=180^0\)(hai góc kề bù)
=>\(x+100^0=180^0\)
=>\(x=80^0\)