Study Guide — 8.G.A.5
Use informal arguments to establish facts about the angle sum and ext…
Name and describe shapes by their defining attributes.
What this standard means
- 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.
- Apply use informal arguments to establish facts about the angle sum and ext… with models and explanation
- Names shapes correctly
_See printable PDF for diagram._
How to use the 20 practice sets
| Sets | When to use | | --- | --- | | 1–5 | Intro — explore together, short written items | | 6–10 | Core skills — diagrams and written practice | | 11–15 | Mixed review — explain thinking | | 16–20 | Stretch — word problems and mastery tasks |
Pacing: 10–15 minutes per session.
How to practice
1. Shape hunt at home — find circles, rectangles, etc. 2. Count sides and corners 3. Sort shapes by attribute
_See printable PDF for diagram._
Common mistakes
- Naming by orientation instead of attributes
- Confusing flat and solid shapes
Review and practice tests
1. Start Review 1/10 when sets 1–3 feel comfortable. 2. Move up one review level with little help. 3. Use Practice Test 4/10–6/10 for mid-standard checks. 4. Practice Test 10/10 is the mastery bar for 8.G.A.5.
- [ ] Names shapes correctly
- [ ] Counts sides and vertices
- [ ] Distinguishes defining from non-defining attributes
Materials for this standard
- Practice Problems — 20 printable sets (computational and word problems)
- Review — 10 difficulty levels
- Practice Test — 10 difficulty levels
- Answer key — for parents and tutors