# Module Focus: Geometry

The focus of the Wednesday morning session for grades 9-10 math was to explore the topics covered in the first two modules of geometry. Congruence is covered in Module 1. The biggest change in geometry with respect to congruence is that two geometric figures are defined to be congruent if there is a sequence of rigid motions that carries one on to the other. Rigid motions are first introduced in grade 8 and teachers might want to take a look at Grade 8 Module 2 and Grade 8 Module 3 to see how the properties of rigid motions were explored. Participants discussed how they currently characterize transformations, and most agreed that they associate transformations with a set of rules and they tend to be very coordinate based. Students now need to develop a deeper understanding of transformations and their purpose without the use of the coordinate plane.

Module 1 starts off with 5 lessons on constructions. Students will be performing the same constructions as in the past, but the focus is on not just the figure being constructed, but the steps behind the construction. Students will need precision with their vocabulary, as they will need to be able to communicate clearly the steps behind the construction for all to understand. Focus is on the construction and instruction.

Topic C in Module 1 covers the transformations and rigid motions studied in 8th grade. The progression of intuitive, to the concrete, to formally defining a transformation is developed. Participants took a look at this progression with the concept of reflection in lesson 14 where students explore what they notice about the line of reflection and perpendicular bisectors. They then tie this exploration back to their work in the opening lessons that dealt with constructing the perpendicular bisectors and angle bisectors. Students are then introduced to the formal definition of reflections.

Topic D introduces the concept of congruence through rigid motion. Lesson 22 is the presentation of the proof by rigid motion for the SAS criteria. Students need to know the properties that are preserved with the transformations that are rigid motions (i.e. distance preserving, angle preserving) and need to be able to communicate these properties while writing proofs that involve the use of rigid motions. Once the congruence criteria (i.e. SAS, SSS, HL) have been proven, they then can be used in proofs for congruence as we saw in lesson 26.

Topic G reviews the content of the modules and reinforces the purpose behind the axiomatic system. A math teacher’s story was told: “We have to cover several chapters from the textbook and there are approximately 40 formulas. I may offer you a deal: you will learn just four formulas and I will teach you how to get the rest out of these formulas.” The students gladly agreed.

Module 2 focuses on similarity and right triangle trigonometry. Scale drawings are first introduced in grade 7 and teachers might want to take a look at the content covered in Grade 7 Module 1 for gap purposes. Scale drawings are approached in the geometry module with two methods, the ratio and parallel method. Participants had fun with the parallel method and using the set square to generate parallel lines. After scale drawings are explored, students go on to study the properties of dilations which sets the tone for proving the similarity criteria for triangles (AA, SAS and SSS).

The remainder of Module 2 focuses on right triangle trigonometry. Lessons 16, 21 and 25 set the foundation for the trig functions without officially using the language. These lessons explore the internal relationships within and between similar triangles and how the ratios of corresponding sides can be used to find missing lengths.

The materials for this session are available here: