Lesson Plan

Danielle Cancelli

Lesson: Angles Within Triangles

Length: 45 minutes

Age or Grade Level Intended: 6th Grade

Academic Standard(s):

Geometry Standard 4

6.4.4 Understand that the sum of the interior angles of any triangle is 180º and the sum of the interior angles of any quadrilateral is 360º. Use this information to solve problems.

Performance Objective(s):

The sixth graders will correctly identify the measures of nine out of ten missing angles of different triangles when given a corresponding worksheet.


Students will be given a worksheet with ten math problems. They will be assessed by the completion and correction of each problem on the worksheet. They will be evaluated by the amount of problems that are answered correctly. If the student correctly answers the problems on the worksheet, full credit will be given. Students will be expected to answer sixteen out of the twenty problems that they are given.

Advance Preparation by Teacher:


Triangle Cutouts


Dry Erase Board

Dry Erase Markers


To prepare for the lesson, make sure that there are enough copies of the worksheet for each student (worksheet is attached). Also make sure that there are enough triangle cutouts for each student. Before the students arrive, write some sample problems on the board (attached) that you will discuss with the students before the worksheet is given to them.



Begin the lesson by reviewing the previous lesson about complementary and supplementary angles. Refresh the students’ memories on how to create both types of angles. Then explain to the students that each triangle has three interior angles that add up to a total of 180º. Do the example problems that are written on the board with the class. Answer any questions they may have regarding those problems or the information that you covered.

Step-by-Step Plan:

  1. Draw the example problems on the dry erase board.
  2. Do the example problems with the entire class. Make sure they understand that for every triangle, the three interior angles sum up to 180º (Bloom Level I Knowledge).
  3. Pass out the triangle cutouts to each student.
  4. Then tell the students to open up their books to the section on Angles In Triangles. There is an activity in the section that explains the sum of all the angles inside of a triangle. Read aloud with the students the directions for the activity. It will help them understand and absorb the information more easily. Explain each step thoroughly with the triangle cutouts (Bloom Level II Comprehension) (Gardner Linguistic):
  5. Label the three corners of the triangle cutout with the numbers 1, 2, and 3. (Bloom Level I Knowledge)
  6. Rearrange the torn pieces so that the corners all meet at one point. Notice that together they form a straight line, which equals 180º (Gardner Logical/Mathematical).
  7. Ask the class if they have any questions on why or how the angles add up to 180º.
  8. Pass out the worksheets to the students. (Attached).
  9. Have the students independently complete(Gardner Intrapersonal) the worksheet problems based on what they have learned and assist those who need help (Bloom Level III Application) (Gardner Logical/Mathematical).


At the end of class, ask the students if they have any questions or need help with understanding the angles within a triangle. If they do need help, spend the last amount of class time working with them. If they do not need help, review what the students learned throughout the class by asking them questions (Bloom Level II Comprehension).


  1. How many angles are there in a triangle?
  2. What do the angles of each triangle add up to?


Was I prepared for the lesson?

Were the students engaged?

What could I have done to improve the lesson?

Did the students easily understand the instructions?

Was there enough time given to complete the lesson?

Did the students learn from the lesson?

Do the students understand that three angles of each triangle sum up to 180º?


Student with ADHD:

  • The hands-on activity will help the student with ADHD stay focused and interested in the lesson.
  • The directions are also brief and to the point. That way the student will be able to keep their focus on the directions and completely understand what they have to do.
  • The lesson includes both verbal and written directions, which means the student has more than one way of receiving information. If he/she doesn’t hear all of the information that is verbally given, there is also written directions that may be followed.
  • Positive reinforcement will also help the student with ADHD because it will give encouragement, if needed.

Name ______

Angles In Triangles

Directions: Two angles of a triangle are given. Find the remaining missing angle.

1. 65º, 25º ______

2. 72º, 80º______

3. 104º, 16º______

4. 90º, 50º______

5. 16º, 74º______

6. 60º, 40º______

7. 43º, 47º______

8. 150º, 15º______

9. 5º, 100º______

10. 25º, 85º______

SAMPLE PROBLEMS (write on dry erase board before class)