I would present triangles to the students after talking about the definition of a polygon. I would first have them define the different types of triangles in their own words. This would let me know their prior knowledge of triangles.

*Triangle*: A polygon with 3 sides.

**Triangles (classified by sides)**

*Equilateral Triangle*: A triangle with 3 congruent sides.

*Isosceles Triangle*: A triangle with 2 congruent sides.

*Scalene Triangle*: A triangle with no congruent sides.

**Triangles (classified by angles)**

*Right triangle*: A triangle with one angle equal to 90°.

*Acute triangle*: A triangle where all angles are less than 90°.

*Obtuse triangle*: A triangle where one angle is greater than 90°.

I would first have them explore the characteristics of each triangle. Some questions:

- Is it possible to have 2 right angles in a right triangle? Why or why not?
- Explain if all angles have to be less than 90° in an acute triangle, why or why not. Illustrate your observations.
- Can you draw an obtuse triangle that have 2 angles greater than 90°? Explain your answer.
- Is it possible for an isosceles triangle to be equilateral, or an equilateral triangle to be isosceles? Why or why not?
- What can we determine about the angles of an equilateral, isosceles, and scalene triangle? Illustrate your findings. Why is this important to know?

I would then have the students compare the triangles, look for similarities and differences among them. We would look at a variety of triangles and have them experiment with classifying them. My objective would be for the student to obtain the knowledge that every triangle can be classified by its angles *and* by its sides. They could explain their knowledge by drawing a diagram to illustrate all possible ways a triangle can be categorized by its sides and angles. At the end, revisit their first definitions and change what they have discovered. A journal entry would also be a nice way to collaborate all the ideas they have developed in their discoveries.

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Julie, These entries look great! Ensuring students have a concrete understanding on the vocabulary is essential. Your plan is well thought out and the questions you have identified will infuse some higher level thinking into a lesson that often is simply presented as a memorization activity. Incorporation of a journal entry will also help solidify the knowledge. Nice Job! Beth

Julie,

This is a great set up and thought process about triangles. I like the idea of a journal entry and having students compare and contrast the types of triangles. Your vocabulary section looks great!

Rachael