Parallel Lines and the Angles in a Triangle
5 min
Teacher Prep
Setup
Narrative
The purpose of this activity is for students to make sense of a diagram they will use in a later activity to justify that the sum of the interior angles of a triangle is 180 degrees.
Launch
Tell students to close their books or devices (or to keep them closed). Arrange students in groups of 2. Display the image of a triangle with two parallel lines for all to see. Use Co-Craft Questions to orient students to the image and elicit possible mathematical questions.
Give students 1–2 minutes to write a list of mathematical questions that could be asked about the situation before comparing questions with a partner.
Student Task
Here is triangle ABC. Line DE is parallel to line AC.
Sample Response
Sample responses:
- What is the measure of angle DBA?
- What is the measure of angle EBC?
- What rigid transformation takes angle DBA to angle BAC?
- What is the sum of a+b+c?
Activity Synthesis (Teacher Notes)
Invite several partners to share one question with the class and record responses. Ask the class to make comparisons among the shared questions and their own. Ask, “What do these questions have in common? How are they different?” Listen for and amplify language related to the learning goal, such as using transformations to show the angle sum of triangles.
Standards
- 7.NS.A·Apply and extend previous understandings of operations with fractions to add, subtract, multiply, and divide rational numbers.
- 7.NS.A·Apply and extend previous understandings of operations with fractions to add, subtract, multiply, and divide rational numbers.
15 min
15 min
Knowledge Components
All skills for this lesson
No KCs tagged for this lesson
Parallel Lines and the Angles in a Triangle
5 min
Teacher Prep
Setup
Narrative
The purpose of this activity is for students to make sense of a diagram they will use in a later activity to justify that the sum of the interior angles of a triangle is 180 degrees.
Launch
Tell students to close their books or devices (or to keep them closed). Arrange students in groups of 2. Display the image of a triangle with two parallel lines for all to see. Use Co-Craft Questions to orient students to the image and elicit possible mathematical questions.
Give students 1–2 minutes to write a list of mathematical questions that could be asked about the situation before comparing questions with a partner.
Student Task
Here is triangle ABC. Line DE is parallel to line AC.
Sample Response
Sample responses:
- What is the measure of angle DBA?
- What is the measure of angle EBC?
- What rigid transformation takes angle DBA to angle BAC?
- What is the sum of a+b+c?
Activity Synthesis (Teacher Notes)
Invite several partners to share one question with the class and record responses. Ask the class to make comparisons among the shared questions and their own. Ask, “What do these questions have in common? How are they different?” Listen for and amplify language related to the learning goal, such as using transformations to show the angle sum of triangles.
Standards
- 7.NS.A·Apply and extend previous understandings of operations with fractions to add, subtract, multiply, and divide rational numbers.
- 7.NS.A·Apply and extend previous understandings of operations with fractions to add, subtract, multiply, and divide rational numbers.