IM G Unit 1 Lesson 19

Mentally evaluate all of the missing angle measures in each figure.

What is the measure of the missing angle?

What is the measure of the missing angles?

What is the measure of the missing angle?

What is the measure of the missing angles?

Diego made the conjecture: “The angle formed between the angle bisectors is always a right angle, no matter what the angle between r and l is.” It is difficult to tell specifically which angles Diego is talking about in his conjecture.
Label the diagram and rephrase Diego’s conjecture more precisely using your labels.

Here are 2 intersecting lines that create 2 pairs of vertical angles:

1. What is the relationship between vertical angles? Write down a conjecture. Label the diagram to make it easier to write your conjecture precisely.

IM G Unit 1 Lesson 19 from IM Geometry by Illustrative Mathematics, https://im.kendallhunt.com/HS/students/2/1/19/index.html. Licensed under the Creative Commons Attribution 4.0 license, https://creativecommons.org/licenses/by/4.0/.

2. How do you know your conjecture is true for all possible pairs of vertical angles? Explain your reasoning.

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