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# Perp Lines are Perfect

Lesson 7 of 9

## Objective: SWBAT find the perpendicular bisector of a line segment and construct perpendicular bisectors using a compass and straight-edge.

#### Do Now

*10 min*

Students will complete two warm-up questions that require them to use pre-requisite skills of writing equations of perpendicular lines and also finding the midpoint of a line segment.

#### Resources

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The student notes provide scaffolded notes and examples for students to complete two constructions of perpendicular lines through a point on a line and a point not on the line. These videos explaining construction from a point on a line and not on a line are a great resource for in-class instruction and also for absent students (MP 5).

CCSS for Geometry requires that students prove how and why constructions work. The construction in this lesson requires students to have knowledge of congruent triangles (the next unit) so teachers should make students that we'll be proving *why these constructions work* in future lessons (MP 7).

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#### Activity/Homework

*10 min*

Student can work on practice question in pairs or small groups. To review, you can ask students to explain how the 3 constructions learned in class today are similar and different. One suggestion is that you may want to ask students to come re-state the steps to these constructions in their own words.

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#### Exit Ticket

*10 min*

Students will find the perpendicular bisector of a line segment given 2 endpoints. This Exit Ticket can easily be collected by asking students to write their work on a separate piece of paper or a post-it note.

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- UNIT 1: Introduction to Geometry: Points, Lines, Planes, and Angles
- UNIT 2: Line-sanity!
- UNIT 3: Transformers and Transformations
- UNIT 4: Tremendous Triangles
- UNIT 5: Three Triangle Topics
- UNIT 6: Pretty Polygons
- UNIT 7: MidTerm Materials
- UNIT 8: Circles
- UNIT 9: 3-D Shapes and Volume
- UNIT 10: Sweet Similar Shapes
- UNIT 11: Trig Trickery
- UNIT 12: Finally Finals

- LESSON 1: Proving It
- LESSON 2: Prove It with Angle Relationships
- LESSON 3: Skew Lines and their Friends
- LESSON 4: PTA (Parallel Lines, Transversals and Angles)
- LESSON 5: Flow Proofs and PTA
- LESSON 6: Line It Up!
- LESSON 7: Perp Lines are Perfect
- LESSON 8: Parabolas and Review of Line-sanity!
- LESSON 9: Assessment for Line-Sanity