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Unit 1 - Lesson 15 - Grade 8: Illustrative Mathematics

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Grade 8 Unit 1
Lesson 15: Adding the Angles in a Triangle
CC BY 2021 Illustrative Mathematics®
Grade 8 Unit 1
Lesson 15: Adding the Angles in a Triangle
CC BY 2021 Illustrative Mathematics®
Lesson: Adding the Angles in a Triangle

Can You Draw It? (Warm Up)

1.

Complete the table by drawing a triangle in each cell that has the properties listed for its column and row. If you think you cannot draw a triangle with those properties, write “impossible” in the cell.

Share your drawings with a partner. Discuss your thinking. If you disagree, work to reach an agreement.

Find All Three (Optional)

Your teacher will give you a card with a picture of a triangle.
2.

The measurement of one of the angles is labeled. Mentally estimate the measures of the other two angles.

Find two other students with triangles congruent to yours but with a different angle labeled. Confirm that the triangles are congruent, that each card has a different angle labeled, and that the angle measures make sense.
3.

Enter the three angle measures for your triangle.

Tear It Up

Images for Launch
Your teacher will give you a page with three sets of angles and a blank space. Cut out each set of three angles.
4.

Can you make a triangle from each set that has these same three angles?

Cool Down: Missing Angle Measures

Missing Angle Measures

In triangle ABC, the measure of angle B is 50 degrees.
5.

Give possible values for the measures of angles A and C if ABC is an acute triangle.

6.

Give possible values for the measures of angles A and C if ABC is an obtuse triangle.

7.

Give possible values for the measures of angles A and C if ABC is a right triangle.