Special angle pairs

29 teachers like this lesson

Print Lesson

Objective

SWBAT identify special angle pairs and determine angle measurements.

Big Idea

Set the foundation for logical reasoning by providing basic proofs of theorems about complementary, supplementary, and vertical angles.

Lesson Author

Jeff Li MTP

New York, NY

Grade Level

Eighth grade

Subjects

Math

supplementary angles

Geometry

Standards

8.G.A.5

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.

MP2

Reason abstractly and quantitatively.

MP3

Construct viable arguments and critique the reasoning of others.

MP7

Look for and make use of structure.

Warm Up

10 minutes

Each day, students complete a Warm Up that usually consists of spiraling the previous day's material, in addition to older material. Warm-up problems also sometimes extend lessons that students have encountered before to more unfamiliar contexts.

In today's warm-up, because it is the first lesson of a new unit, I review the Homework instead to maximize time in introducing a new concept. The HW on a unit assessment day is generally spiraled review of previous topics, so it is a nice review of older material that improves retention over the course of the year.

Play of the Day

40 minutes

Huddle

10 minutes

For the huddle for this lesson, I really like to go over Silver Problem 5 in detail. The primary lesson I want them to learn is the elegant logical structure that underlies the whole endeavor of geometry. I push students to not only identify the correct answers, but the logic behind each measurement. I also make clear that there is more than one way to prove the measure of each angle... another beautiful element in math.

In this particular problem, I really stress the vocabulary to identify each angle. Getting kids fluent in the vocabulary of, especially, congruent and supplementary, is absolutely critical as this unit develops. I keep pushing kids until they use the correct vocabulary, and then sometimes I even do an activity where I have kids close their eyes and I say something related to the definition, and they call out the vocabulary words.

For example:

Me: Angles that sum to 180 degrees.

Students: Supplementary!

Me: Angles that are opposite of each other and congruent.

Students: Vertical!