Download 8.G.A.5. Use informal arguments to establish facts about the angle

8.G.A.5. 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 angleangle 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.
PARCC Assessment Limit/Clarification:
This standard is part of the major content cluster assessed on PARCC.
Web Resources:
http://illustrativemathematics.org/standards.k8
This link has illustrations that link to tasks to support standard 8.G.5. Simply click on Geometry, 8th grade,
then on the illustrations link.
http://www.mathopenref.com/polygonexteriorangles.html
This link allows students to manipulate a polygon and observe the relationships between the sum of
exterior angles.