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: Triangle
$${{{CDE}}}$$
underwent a transformation that created triangle
$${{{C'D'E'}}}$$
.
[IMG]
a.   Describe how triangle
$${{{CDE}}}$$
was transformed to become triangle
$${{{C'D'E'}}}$$
.
b.   What features stayed the same?
c.   What features changed?
d.   Is triangle
$${{{CDE}}}$$
congruent to triangle
$${{{C'D'E'}}}$$
? Explain how you know.


aligns: no