Activating Strategy

Now, let’s look at the angles in the equilateral triangle. I notice that all of the angles are acute. Remember that we classify triangles by the length of their sides and the type of angles.

The equilateral triangle also has 3 acute angles, which is why it is called an Acute Triangle.

Remember, we have also been identifying and drawing lines of symmetry. To continue this practice, let’s identify and draw the lines of symmetry in this triangle.

So, to summarize, this triangle can be classified as equilateral.  All of the sides are the same length or congruent. ‘Equi’ means equal or the same, and ‘lateral’ means sides.  All three interior angles are acute, so this equilateral triangle can also be classified as an acute triangle. 

Now, let’s look at a different type of triangle called an isosceles triangle. An isosceles triangle has two equal or congruent sides.  Let’s use the Anglegs to create an isosceles triangle.

This triangle can be classified as isosceles because two sides are the same length. Remember, if the Anglegs are the same color, they are congruent.

We have classified this triangle based on the length of the sides, so now, let’s look at the types of angles. I noticed that the triangle has two acute angles and one right angle (the right angle can be justified by placing a color tile at the angle, an index card, or a protractor). A right angle is formed by the perpendicular intersection of two line segments (sides) of the triangle.

I also see that this triangle has one line of symmetry.

This isosceles triangle has one right angle.  Since the triangle has a right angle, it is classified as a right triangle.

To summarize, this triangle has two congruent sides, which is called an isosceles triangle. It also has one right angle, which is called a right triangle.

Finally, let’s use the Anglegs to build a scalene triangle. A scalene triangle has no equal sides. All of the sides are different lengths.  That means I need to use three different-colored Anglegs.

Notice that each side of the scalene triangle is a different length.  I wonder if I can use the Anglegs to create a different scalene triangle.

Guided Practice

Mathematicians, it is your turn to try!

I would like you to have a chance to classify these triangles based on their angles. Turn and talk with your elbow partner.  What do you notice about the angles of these two scalene triangles?

How are the angles in these two scalene triangles the same? How are they different?

Turn and talk with your elbow partner about your noticings.  

Be ready to share your noticings about the angles.  

In summary, we can classify triangles and other two-dimensional figures based on their attributes.  We can observe and record their similarities and differences, and how the figures are alike and different.  

Comparing and contrasting the attributes of the different triangles helped us understand and determine their classifications.

Anchor Chart Classifying Triangles

Four Corners Game

Each room corner is labeled A, B, C, or D. 

• Listen as the teacher presents a question or statement to the class.  

• Responses with a triangle image has been placed in each classroom corner for this task. 

• Express your response by standing in front of one of four choices in each corner of the room.  

• Discuss with each other why you have chosen that particular response.  

REMEMBER: Be ready to present a summary of your responses.

1. FRECKLE - Complete THREE Freckle Assignments each week. DUE FRIDAY. Your HIGHEST score in Targeted Practice is your weekly math grade - Click HERE for Freckle website

• GRADED Targeted Practice - Current skill (5 questions; Score Goal=80% or higher)

• Fact Practice - Multiplication Fact Practice

• Adaptive Practice - At YOUR level

2. iREADY Math - Complete 30 minutes at your level each week