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: Circle
$$A$$
is shown below.
[IMG]
Draw two diameters of the circle.
Identify the shape defined by the end points of the two diameters.
Explain why this shape is always the result.


aligns: no