$\text{Kẻ Ox // AB}$ $\\$ $\Rightarrow$ $\widehat{A}$ + $\widehat{O_1}$ = $180^\circ$ $\\$ $\Rightarrow$ $m^\circ$ + $\widehat{O_1}$ = $180^\circ$ $\\$ $\Rightarrow$ $\widehat{O_1}$ = $180^\circ$ - $m^\circ$ $\\$ $\text{Mà}$ $\widehat{O_1}$ + $\widehat{O_2}$ = $36^\circ$ - ($m^\circ$ + $n^\circ$) $\\$ $\Rightarrow$ $\widehat{O_2}$ = $360^\circ$ - $m^\circ$ - $n^\circ$ - ($180^\circ$ + $m^\circ$) $\\$ $\Rightarrow$ $\widehat{O_2}$ = $180^\circ$ - $n^\circ$ $\\$ $\Rightarrow$ $\widehat{O_2}$ + $\widehat{C}$ = $180^\circ$ - $n^\circ$ + $n^\circ$ = $180^\circ$ $\\$ $\Rightarrow$ $\text{Ox // CD}$ $\\$ $\Longrightarrow$ $\text{AB // CD (cùng song song với Ox)}$
