Common Core · Grade 8
8.G.A.5
Grade 8 — Use informal arguments about the angles created when a transversal crosses parallel lines.
Grade 8 — Establish facts about the angle sum and the exterior angle of triangles.
The 3 skills that cover it
- AnglesMeasure and classify angles, and use complementary, supplementary, vertical and parallel-line relationships to find unknown angles.Read the lesson →
- TrianglesClassify triangles, use the 180-degree angle sum, and apply the triangle inequality and exterior angle theorem.Read the lesson →
- Parallel Lines & TransversalsName the angle pairs a transversal makes with two lines, use them to find unknown angles when the lines are parallel, and use them backwards to prove that two lines are parallel.Read the lesson →
What a student should be able to do
- Classify angles as acute, right, obtuse or straight.
- Use complementary and supplementary relationships to find an angle.
- Apply vertical angle and linear pair relationships.
- Find angles formed when a transversal crosses parallel lines.
- Classify triangles by sides and by angles.
- Find a missing angle using the 180-degree angle sum.
- Apply the exterior angle theorem.
- Decide whether three lengths can form a triangle.
- Name corresponding, alternate interior, alternate exterior and co-interior angle pairs.
- Find unknown angles when a transversal crosses two parallel lines.
- Decide from one angle pair whether two lines are parallel.
- Solve for a variable in an algebraic angle relationship and relate perpendicular lines to right angles.