In this lesson plan on math geometry, angle types should be taught through discovery learning. Rather than teaching students the difference between the three main types of angles, you can let them discover the three types of angles themselves. Students may work in pairs for the majority of this lesson.

## Objectives

At the conclusion of this lesson plan, students should be able to successfully do the following:

- identify the three main types of angles
- give examples of an acute, obtuse, and right angle

## Materials

- Cardboard
- Paper fastener
- Scissors

## An Introductory Activity

Give each pair of students two pieces of cardboard and show them how to connect them at their corners by a paper fastener (brad). This makes an angle manipulative that students can use in order to form any type of angle. Draw a picture of an acute angle and a picture of an obtuse angle on the board, but do not label them. Ask students to work in pairs to figure out which types of angles look more like the first one on the board and which ones look more like the second one. Challenge them to find any angles that don't look like either of them.

Students will likely discover that between 0 and 90 degrees, the angles seem to resemble the first (acute) angle, and between 90 and 180 degrees, the angles seem to resemble the second (obtuse) angle. They may also find that three angles do not resemble either angle – 0, 90, and 180.

## Direct Instruction

After students have shared their findings, you can introduce them to the names of the three main types of angles – acute, obtuse, and right. (You may want to mention that the 0-degree and 180-degree angles are not included in any of these categories.) Have students use their manipulatives to model the various types of acute and obtuse angles, as well as to form a right angle. You may also allow them to discuss tricks they can use to remember the names of the three types of angles.

## Class Review

To get kinesthetic learners more interested in these three types of angles, you can have the students do sit ups to make themselves into the three types of angles. When they are lying down with their knees bent, they form an obtuse angle. When they sit up partway, they form a right angle. When they complete the sit up, they form an acute angle. Guide students in doing several sit ups while chanting "Obtuse, right, acute! Obtuse, right, acute!" This will drill the meanings of the words into their heads.

## Paired Practice-An Extension Activity

In pairs, instruct students to look around the room and find various angles in the classroom, such as the corner of the blackboard, the legs of a chair, or the opening of a slightly open cabinet. Have them sort these angles into one of the three categories. Discuss the fact that most of the angles that they found were probably right angles, as well as why this might be so.

## Assessment

You can assess whether students have understood the concept of the three main types of angles by looking at the results of their paired practice work. Make sure that students can adequately differentiate between acute, right, and obtuse angles.

In this lesson plan on math geometry, angle types are presented as extremely limited. You can also teach students about the differences between complementary and supplementary angles, so that they understand the different classifications that angles can have.

## This post is part of the series: Activities and Lesson Plans for Geometry: Teaching Angles

- Math Geometry Lesson on Angle Types
- Geometry Lesson Plan: Supplementary and Complementary Angles
- Geometry Activities: Fun With Angle Bisectors
- Angles and Shapes: A Geometry Lesson Plan Elementary Students Will Love!