Talking About Triangles
Lesson 3 of 4
Objective: SWBAT identify characteristics of triangles.
Following the established Start At/ Stop At Routine, I have a student choose a number from the 16-30 envelope as the start at number and a number from the 1-15 number as the Stop At Number. Then have a student lead the class in counting back on the number line.
Teacher's Note: You will need a set of POWER POLYGONS for each student. These can be ordered through any math catalog company or online.
I start the lesson by having each student sit at a table. The flat surface will make working with these shapes much easier. I hand each student a set of the shapes and ask them to look through the shapes. I give them a few minutes to explore them. After the exploration time, I ask them to tell me some things they notice about the shapes. Then I ask them to pull out all of the triangles and separate them from the other shapes.
I continue the lesson by asking my students, "What do you remember about triangles?" Here, I want them to recall information from a previous discussion. I expect that as a group they will recall all of the features in their own words. Then, I will ask them to use this information to double check that all of their shapes are triangles. The Common Core requires that students distinguish between the defining attributes of geometric objects (CCSS.Math.Content.1.G.A.1). As they work on this task, my students are also critiquing the reasoning of others and constructing a rationale of what makes each shape a triangle (CCSS.Math.Practice.MP3). There is a quick video of some students performing this activity in the accompanying reflection, It kinda looks like a triangle.
As the discussion of features continues, I will introduce the term vertices as a substitute for corners, the term my students typically use when we first discuss triangles. I like to introduce new vocabulary as a substitute for a shared term, so students initial understanding is connected.
I want to introduce two new activities that the students can do during math workshop today. The first activity will be making triangles on a Geo Board. I ask for volunteers to demonstrate how to create these on a Geo Board.
The second activity will require the use of Array Paper. I launch this activity by asking my students to shut their eyes and visualize a triangle. I ask them to think about how many sides and how many vertices a triangle has. Then I ask them to open their eyes and to draw the triangle in the air. I then show them the array paper and tell them that they will use this paper to draw triangles. I ask again how many vertices a triangle has? Once they answer, I explain that I want each student to circle three dots on the array paper. These dots will be the vertices of a new triangle. I will demonstrate this by selecting dots and connecting my circled dots to form a triangle.
Then, I give the students a challenge:
Your job is to draw as many triangles on the Array Paper as you can.
There are three activities that the students can choose from today. All three were introduced in the beginning of this lesson, so that students can choose the activity that most interests them first
1. Power Polygons: The students can sort and classify the shapes in different ways.
2. Creating Geo Board Triangles: Use Geo Boards and bands to create triangles.
3. Triangles on Array Paper: Use the array paper (previous section) to create as many triangles as you can. View the video, Drawing Triangles, in the section resource to see this in action.
I have provided two examples of student work on the Array Paper. Student Work Making Triangles is an image of a completed sheet. In this case, the student has forgotten to describe how many triangles that she made. Riley working on Array Paper demonstrates an interesting idea, for Riley is making congruent triangles, recognizing that it is efficient to make a lot of triangles by repeating the pattern of dots that are selected.
Today, we will likely continue to work on centers until it is time to move on to the next activity. This will allow me to check in with students individually.