Use the parallelogram from Example 1 to verify that the opposite angles in a parallelogram are congruent and consecutive angles are supplementary given that [math]\overline{AD}\parallel\overline{BC}[/math] and [math]\overline{AB}\parallel\overline{DC}[/math].

[list=1][br][*]Extend the lines in the parallelogram to show two pairs of intersecting lines and label the angles with numbers.[br][*]Prove [math]\angle 4 \cong\angle 9[/math].[br][*]Prove [math]\angle 7 \cong\angle 14[/math].[br][*]Prove that consecutive angles of a parallelogram are supplementary.[br][/list][br][br]This applet is provided by Walch Education as supplemental material for their mathematics programs. Visit www.walch.com for more information.