Question

A classmate says that line AB is parallel to line DC according to the diagram. Explain the classmates error. (Look at picture question 23)

Answer 1

Referring to the diagram for lesson check (#22 and #23), we see a quadrilateral ABCD for which angles D and C are supplementary.

The transversal being DC, the parallel lines are therefore DA and CB.

The classmate did find two lines that are opposite sides of the quadrilateral, but the parallel lines should be intersected by the transversal, instead of the transversal (DC) itself.