Unit Plan 16 (Grade 4 Math): Angle Addition & Unknown Angles

Focus: Use angle measure additivity to find unknown angles; represent with equations and justify with diagrams.

Grade Level: 4

Subject Area: Mathematics (Measurement & Data — Angle Measurement)

Total Unit Duration: 5 sessions (one week), 45–60 minutes per session

I. Introduction

Students learn that angle measure is additive: a larger angle can be decomposed into smaller adjacent angles whose measures sum to the whole. They apply this idea to find unknown angles by writing and solving equations that match diagrams.

Essential Questions

• How can breaking a larger angle into smaller parts help me find an unknown angle?
• How do I write an equation that exactly represents an angle diagram?
• When should I use 90 degrees (right angle) or 180 degrees (straight line) as a benchmark?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Explain and use the angle addition rule to decompose and compose angles.
2. Write equations with a symbol for the unknown to represent angle relationships in diagrams.
3. Use benchmark angles (right and straight) to check reasonableness of solutions.
4. Communicate solutions with precise units (degrees), labels, and clear diagrams.
5. Critique the reasoning of peers and revise work based on feedback.

Standards Alignment — CCSS Grade 4

• 4.MD.7: Recognize angle measure as additive; find unknown angles on a diagram by using equations with a symbol for the unknown.
• Connections: 4.MD.5–4.MD.6 (angle and degree concepts; measuring) as needed for review.

Success Criteria — Student Language

• I can decompose a larger angle into parts and explain how the measures add.
• I can write an equation that matches an angle diagram and solve for the unknown.
• I can use benchmarks (90 and 180 degrees) and units to check if my answer makes sense.
• I can defend my reasoning with a labeled diagram and clear explanation.