Discussion Question 4 (Solution)

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Download the GeoGebra file: http://www.geogebratube.org/material/download/format/file/id/42709


\[\angle BAN + \angle BMN = 180^\circ {\rm{ \;(}}\angle {\rm{s\;in\;opp\;segments)}}\]
\[\angle CMN + \angle BMN = 180^\circ {\rm{ \;(adj }}\;\angle {\rm{s\;on\;a\;str\;line)}}\]
\[\therefore \angle BAN = \angle CMN\]
\[\angle CDN + \angle CMN = 180^\circ {\rm{ \;(}}\angle {\rm{s\;in\;opp\;segments)}}\]
\[\therefore \angle CDN + \angle BAN = 180^\circ\]
\[{\rm{In\;fact, }}\;AB\;{\rm{ is\;parallel\;to }}\;DC.{\rm{ \;(int }}\;\angle {\rm{s)}}\]