## Reflection: Coherence Complementary & Supplementary Angles - Section 4: Closing

At the end of our lesson today, one student pointed out, "complementary angles have to make a square, not a rectangle." This was an aha moment for me! When creating the investigation pages, I used squares to model complementary angles and rectangles to model supplementary angles. I should have used one or the other for both types of angles!

To counteract this misconception, I completed the following steps:

1. I drew a right angle using two rays and then decomposed the angle into two acute angles. I then asked: Are these complementary? Students said, "Yes."

2. Then I drew a square, decomposed a right angle in the square, and asked: Are these complementary?  Students said, "Yes."

3. Finally, I drew a rectangle, decomposed a right angle in the rectangle, and asked: Are these complementary?  Students said, "Yes."

4. I asked: Why? Because they all decompose what type of angle? Students said, "a right angle."

Then, we connected this idea to the supplementary angles and how the dividing line decomposes 180 degree angle instead of decomposing a 90 degree angle.

Aha Moment
Coherence: Aha Moment

# Complementary & Supplementary Angles

Unit 8: Geometry
Lesson 2 of 7

## Big Idea: Through an exploration process, students will practice using a protractor, recording observations, and constructing definitions for complementary and supplementary angles.

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Standards:
Subject(s):
Math, supplementary angles, angles, Triangles, angles (Constructions), quadrilateral, complementary angles, acute angles, right angles, adding angles, measuring angles, obtuse angles, Polygon, shapes, classifying triangles
110 minutes

### Kara Nelson

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