standard_description: Prove theorems about triangles. Theorems include: measures of interior angles of a triangle sum to 180°; base angles of isosceles triangles are congruent; the segment joining midpoints of two sides of a triangle is parallel to the third side and half the length; the medians of a triangle meet at a point.
problem_activity: Task
Suppose $\overline{AB}$ is a line segment and $D$ is a point not on $\overline {AB}$ as pictured below:
[IMG]
Let $C$ be the point so that $|CD| = |AB|$, $\overleftrightarrow{CD}$ is parallel to $\overleftrightarrow{AB}$, and $ABCD$ is a quadrilateral.
Draw a picture of this situation and
show that $ABCD$ is a parallelogram.


aligns: no