Mary Beth has taught 1st, 4th and 5th grade and has a specialist degree in Educational Leadership. She is currently an assistant principal.
By the end of the lesson, students will be able to:
- Differentiate between isosceles triangles and other types of triangles
- Draw an isosceles triangle using a ruler and protractor
- Determine the measurement of the apex and second base angle in an isosceles triangle
Draw (freehand, with ruler and protractor, and with technology) geometric shapes with given conditions. Focus on constructing triangles from three measures of angles or sides, noticing when the conditions determine a unique triangle, more than one triangle, or no triangle.
- Copies of What is an Isosceles Triangle? - Definition, Properties & Theorem (one per student)
- Multiple triangles cut out of construction paper (both isosceles and non-isosceles)
- Small empty trash can (could also use a box marked 'Trash')
- Small empty treasure chest (could also use a box marked 'Treasure')
- Rulers (one per student)
- Protractors (one per student)
- Copies of the quiz (one per student)
- Blank paper
What is an Isosceles Triangle? Activity
- Students will read the section 'What is an Isosceles Triangle?' silently.
- Have them turn and talk with a neighbor to summarize what they read.
- Circulate the room and check for understanding.
- Display the trash can and treasure chest. Tell the students that they are going to go on a treasure hunt for isosceles triangles in a game called 'Trash or Treasure?'.
- Distribute rulers to students.
- Sprinkle the triangles all over the table or floor. The goal is to be able to pick up and put away as many triangles as possible. If the triangle is isosceles, it goes in the treasure chest. If it is not isosceles, it goes in the trash can.
Properties of Isosceles Triangles Activity
- Students will read the section 'Properties of Isosceles Triangles' silently.
- Pair students with their neighbor to share what they learned, while you circulate.
- Ask if there are any questions before moving to the activity.
- Take the isosceles triangles out of the treasure chest and distribute them to students. Distribute protractors to students, as well.
- Have students measure one base angle and record its measurement on the triangle.
- Now, students will exchange triangles with a peer and practice finding the other base angle and apex measurement without a protractor.
- They can use the text as a reference.
- Have students switch triangles several times to get more practice.
Isosceles Triangle Theorem Activity
- Have students read the remainder of the lesson.
- Ask students what the three theorems are, writing their answers on the board.
- Now have students draw three isosceles triangles on blank paper, using the ruler and protractor.
- Have them use each of the triangles that they drew to prove each of the three statements in the theorem of an isosceles triangle.
- Now, partner students and have them model how each of the three statements are true through demonstrating them on their triangles.
- Ask if students have any questions before moving on to the quiz.
- As a formative assessment, students will take the quiz to demonstrate mastery.
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