This document outlines a 50-minute lesson plan for 7th grade students focusing on classifying triangles by angles and sides. It includes an overview of triangle properties, instructional materials, and specific activities such as warm-up questions, guided practice, and independent practice. The lesson aims to familiarize students with triangle types and angles while meeting specific educational standards.

1. Angles and Triangles
Terry Scates
Newton, Kansas

2. Instructor Notes
• Subject Area(s): Math
• Grade level: 7th
grade
• Lesson Length: 50 minute class period
• Synopsis: Name triangles by angles and sides.
• Objective/goals: Students will classify triangles
according to types or angles and sides.
(This PowerPoint presentation was designed as a supplemental piece to the
presentation entitled Classifying Triangles by James Wiens for students in
the special education math class.)

3. • Standard: ▲ identifies angle and side properties of triangles and
quadrilaterals (KS standard 7.3.1.k3)
• Pre-requisite skills: Vocabulary – Acute, Obtuse, Right, Equilateral,
Isosceles, Scalene
• TurningPoint functions: standard question slides
• Materials: All instructional points and practice problems are provided
within the power point slides. Practice questions are designed to be used
with the TurningPoint clickers.
(This PowerPoint presentation was designed as a supplemental piece to
the presentation entitled Classifying Triangles by James Wiens for
students in the special education math class.)
Instructor Notes

4. Lesson Outline
1. Warm-up: Angle classification
2. Setting the Stage:
3. Guided practice:
Turning Point Questions
4. Independent practice: Paper & pencil
5. Closure: Write about triangles

5. What we already know about
angles:
An angle has two sides that share
a common endpoint.

6. What we need to know about
angles:
The point where the sides meet is
called the vertex.

7. What we need to know about
angles:
• Angles are measured in degrees,
where 1 degree is one of 360 equal
parts of a circle.

8. Angles are classified according
to their measure.
An acute angle is less than 90°
An obtuse angle is more than 90°
A right angle is 90°

9. Right Angle
Find some examples of right angles in the classroom:

10. Acute Angle
Find some examples of acute angles in the classroom:

11. Obtuse Angle
Find some examples of obtuse angles in the classroom:

12. Classify this angle:
a) Acute
b) Right
c) Obtuse
Classify this angle:
Countdown
Countdown
10

13. Classify this angle:
a) Acute
b) Right
c) Obtuse
Countdown
Countdown
10

14. Classify this angle:
a) Acute
b) Right
c) Obtuse
Countdown
Countdown
10

15. What we already know about triangles:
• A triangle is a figure with three sides and
three angles.
• The symbol for triangle is

16. What we need to know about triangles:
• The sum of the measures of the angles of
a triangle is 180°.
• You can use this to find a missing angle
measure in a triangle.

17. Triangles can be classified by the
measures of their angles.

18. • An acute triangle has three acute angles.

19. • An obtuse triangle has one obtuse angle.

20. • A right triangle has one right angle.

21. Triangles can also be classified by
the lengths of their sides.

22. • Sides that are the same length are
congruent segments and are often
marked by tick marks.

23. • In a scalene triangle, all sides have
different lengths.

24. • An isosceles triangle has at least two
congruent sides.

25. • An equilateral triangle has all three sides
congruent.

26. Classify this triangle
by angles and by sides
1. Acute / Isosceles
2. Obtuse / Isosceles
3. Acute / Scalene
4. Obtuse / Scalene
4
7
7
70
70
40
Countdown
Countdown
10

27. Classify this triangle
by angles and by sides
4
8
90
60
30
9
1. Acute / Isosceles
2. Right / Isosceles
3. Acute / Scalene
4. Right / Scalene
Countdown
Countdown
10

28. Classify this triangle
by angles and by sides
1. Acute / Isosceles
2. Obtuse / Isosceles
3. Acute / Scalene
4. Obtuse / Scalene
6
14
18
130
35
15
Countdown
Countdown
10

29. Classify this triangle
by angles and by sides
7
7
7
60
60
60
1. Acute / Isosceles
2. Right / Isosceles
3. Acute / Equilateral
4. Obtuse / Scalene
Countdown
Countdown
10

30. You are ready to try on your own!
• Think about what you have learned.
• Think about what you already knew.
• Think about what you can teach others.

31. Independent Practice

32. Independent Practice

33. Answer Key for
Independent Practice
A. Obtuse / Isosceles
B. Acute / Equilateral
C. Right / Isosceles
D. Acute / Isosceles
E. Obtuse / Isosceles
F. Acute / Equilateral
G. Obtuse / Scalene
H. Right / Scalene

34. Closure/Summary
• Is the sum of the angles of an obtuse
triangle greater than the sum of the angles
of an acute triangle? Explain your answer.

35. References
Glencoe McGraw-Hill Math Connects
Course 2, Study Guide and Intervention
and Practice Workbook, 2008.
Wiens, James, Classifying Triangles,
PowerPoint presentation, November 2008.