Đáp án+Giải thích các bước giải:
Vì a//c (gt) nên:
$\widehat{N_1}$+$\widehat{O_1}$=$180^0$ (trong cùng phía bù nhau)
$130^0$+$\widehat{O_1}$=$180^0$
$\widehat{O_1}$=$180^0$-$130^0$
$\widehat{O_1}$=$50^0$
Ta có:
$\widehat{O_1}$+$\widehat{O_2}$=$100^0$ (gt)
$50^0$+$\widehat{O_2}$=$100^0$
$\widehat{O_2}$=$100^0$-$50^0$
$\widehat{O_2}$=$50^0$
Vì b//c (gt) nên:
$\widehat{O_2}$+$\widehat{M_1}$=$180^0$ (trong cùng phía bù nhau)
$50^0$+$\widehat{M_1}$=$180^0$
$\widehat{M_1}$=$180^0$-$50^0$
$\widehat{M_1}$=$130^0$
Vậy $\widehat{M_1}$=$130^0$
