Acute, Obtuse, and Right Angles

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Students will be able to identify acute, obtuse, and right angles.

Big Idea

Kinesthetic activities help when reviewing our angle types.


10 minutes

I open this lesson, which is a review of 4th grade standard 4.G.1, by sharing student friendly definitions of the words obtuse, acute, and right angle and then giving the students motions to represent each of these words. 

In my classroom I consistently put motions with words.  I think it is a good strategy not only for English language learners but for all students. We remember best what we "do", and using our bodies to create representations of shapes is another way to make the vocabulary "stick". 

Each arm is a representation of a line (two lines are needed to make an angle).  Students make an obtuse angle by using both of their hands and then use a deep, groggy voice for saying obtuse angle.  The word goes with the motion and they are done simultaneously. 

For acute, as students make an acute angle with their hands they use a high-pitched, mousey voice to say acute angle. 

For a right angle, students make a right angle with their arms and use a normal voice to say right angle.  After introducing all three words we use a Simple Simon method of practicing the motions along with the vocabulary words. 


30 minutes


Students work as individuals to find their match, after index cards with definitions, examples of angle measures, and pictures of angles within polygons are passed out. They have about a minute to find their group.

Once students establish a group that they belong to, they then work in their group to discuss the meanings of their new math terms.   They should be discussing the definitions while matching them to examples within their group.  After groups are finished the cards should be collected, shuffled and redistributed so that the activity can be repeated.  This will give the students an additional practice of using the definitions and viewing the examples. 

I suggest dividing the total number of students by 3 to determine how many cards are needed to evenly divide students.  


10 minutes

We close with a vigorous review, with motions, of the three angle types. As an exit slip the students label and define three angles. 

I model three examples of angles of appropriate responses to the 3 different activity task. For example, given a polygon card I identify the angle type and write the definition.

I then provide each student with one the index cards used in the previous activity.  Depending on what card the student has, s/he determines the two other elements (angle type, a definition of the angle, or representation of the angle within a polygon).

Students use a blank index card to create their final product, which should show a polygon, with angle identified and labeled, and a written definition. By using multiple modalities, students acquire their mathematical vocabulary more rapidly. This lesson, however, is not the end of explicit angle vocabulary instruction. These words will now be used, in context, during speaking and writing to ensure that they become a part of the students' thinking.