Name: Identify the Triangle
Grades: 9-12
Class: Geometry
Rationale:
In Geometry, students should be able to classify triangles based on side lengths and angles. In this lesson, students will be exposed to a variety of clues that aid students developing problem solving skills and mathematical vocabulary. Students will demonstrate understanding of the different classification of triangles. Identification of triangles is not only important for higher mathematical thought, but for practical applications. During the lesson, students will be expected to work in pairs or small groups and communicate ideas, and justify their thinking.
Essential Question
What are the different ways to classify a triangle?
Objectives
· Students will identify and classify acute, obtuse, right, equiangular, equilateral, isosceles, and scalene triangles.
Materials
· Worksheets 1 and 2 (3 Optional)
· Answer Key
· ELMO
· Popsicle Sticks
· Math Journals/Line Paper
· Projector/Whiteboard
Anticipatory Set
Have students take out their math journals and respond to the prompt. Read the prompt to the class and give students approximately five to eight minutes to response to the writing prompt.
In Geometry we have identified and classified different types of triangles. What are the names of the types of triangles we have identified? What characteristics are unique to each type of triangle?
Have students share their response with a partner and ask pairs to inform each other of any missing information that needs to be included in the response. Missing information should be added to response.
Model
With popsicle sticks, the teacher and students will model the different types of triangles. Check for understanding and review if required. Use ELMO to model triangle for the class.
Guided Practice
Students will participate in a crime scene investigation to identify the triangle that committed the crime of stealing the school’s mascot. Provide students with a list of suspects (Worksheet 1) and clues (Worksheet 2). The clues provide students with information about the angles and side lengths of the triangle that committed the crime. Each clue may identify more than one triangle. Students should list all the types of triangles the clue applies to. To determine the triangle that committed the crime, students will total up the type of triangle that appears the most.
To make the investigation more engaging, create a crime scene in your classroom using yellow tape. Then hide the clues throughout classroom or building if possible. Instead of giving students the list of clues, provide students with a blank list of clues, and explain to them the number of clues they must fine (Worksheet 3).
Checking for Understanding:
In a quick write, have individual students explain which triangle they think committed the crime and why. Use students’ responses to determine level of understanding.
**THIS LESSON CAN ALSO BE MODIFIED TO BE USED WITH QUADRILATERALS**
Worksheet 1
Triangle Investigation: Suspects
Name:______Date______
Worksheet 2
Triangle: Clues
Name:______Date______
The Crime Scene Investigation Unit needs your help. Recently, someone broke into the school and stole the school’s mascot. The investigation team has discovered the following clues, but need your help identifying the suspect. Read each clue and determine from the suspect list which triangle(s) meets the characteristics provided in the clue. After you have processed all the clues, identify the triangle that stole the school’s mascot by tallying up the results. The triangle suspect that has the most tally marks is your culprit.
1. The sum of the interior angles of the suspect is 180⁰______
2. One clue left showed exactly two sides of the triangle are the same length______
3. A clue showed that all of the angles are larger than 40⁰______
4. The suspect has three sides______
5. A clue left showed a triangle with an angle measure of 60⁰______
6. At least two of the angles are congruent______
7. One clue left showed that A2+B2≠C2______
8. The suspect has exactly 2 acute angles______
9. A clue left showed a triangle with an exterior angle of 130⁰______
10. The suspect has at least one angle 100⁰ or bigger______
TALLY
1 / 2 / 3 / 4 / 5 / 6 / 7The Suspect is______
Worksheet 3
Triangle: Clues
Name:______Date______
The Crime Scene Investigation Unit needs your help. Recently, someone broke into the school and stole the school’s mascot. The investigation team has discovered the following clues, but need your help identifying the suspect. Read each clue and determine from the suspect list which triangle(s) meets the characteristics provided in the clue. After you have processed all the clues, identify the triangle that stole the school’s mascot by tallying up the results. The triangle suspect that has the most tally marks is your culprit.
1. Clue 1: ______Suspects:______
2. Clue 2: ______Suspects:______
3. Clue 3: ______Suspects:______
4. Clue 4: ______Suspects:______
5. Clue 5: ______Suspects:______
6. Clue 6: ______Suspects:______
7. Clue 7: ______Suspects:______
8. Clue 8: ______Suspects:______
9. Clue 9: ______Suspects:______
10. Clue 10: ______Suspects:______
TALLY
1 / 2 / 3 / 4 / 5 / 6 / 7The Suspect is______
ANSWER KEY
Triangle: Clues
Name:______Date______
The Crime Scene Investigation Unit needs your help. Recently, someone broke into the school and stole the school’s mascot. The investigation team has discovered the following clues, but need your help identifying the suspect. Read each clue and determine from the suspect list which triangle(s) meets the characteristics provided in the clue. After you have processed all the clues, identify the triangle that stole the school’s mascot by tallying up the results. The triangle suspect that has the most tally marks is your culprit.
1. The sum of the interior angles of the suspect is 180⁰: 1, 2, 3, 4, 5, 6, 7
2. One clue left showed exactly two sides of the triangle are the same length: 1, 3, 6
3. A clue showed that all of the angles are larger than 40⁰: 3, 5, 6
4. The suspect has three sides: 1, 2, 3, 4, 5, 6, 7
5. A clue left showed a triangle with an angle measure of 60⁰: 2, 5, 7
6. At least two of the angles are congruent: 1, 3, 5, 6
7. One clue left showed that A2+B2≠C2: 1, 2, 3, 4, 5
8. The suspect has exactly 2 acute angles: 1, 4, 6, 7
9. A clue left showed a triangle with an exterior angle of 130⁰: 2, 4
10. The suspect has at least one angle 100⁰ or bigger: 1, 4
TALLY
1 / 2 / 3 / 4 / 5 / 6 / 77 / 5 / 6 / 6 / 6 / 6 / 4
The Suspect is Triangle 1: Obtuse Isosceles Triangle