standard_description: Use informal arguments to establish facts about the angle sum and exterior angle of triangles, about the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles. For example, arrange three copies of the same triangle so that the sum of the three angles appears to form a line, and give an argument in terms of transversals why this is so.
problem_activity: Identify whether the following statements are true or false.
a.   A parallelogram is always a trapezoid. T / F
b.   A quadrilateral is always a parallelogram. T / F
c.   A parallelogram is always a polygon. T / F


aligns: no