Angles and Triangles

Terry Scates Newton, Kansas

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.)

• 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

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

What we already know about angles:

An angle has two sides that share a common endpoint.

What we need to know about angles:

The point where the sides meet is called the vertex.

What we need to know about angles:

• Angles are measured in degrees, where 1 degree is one of 360 equal parts of a circle.

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°

Right Angle

Find some examples of right angles in the

classroom:

Acute Angle

Find some examples of acute angles in the classroom:

Obtuse AngleFind some examples of obtuse angles in the

classroom:

Classify this angle:

a) Acute

b) Right

c) Obtuse

Classify this angle:

CountdownCountdown

10

Classify this angle:

a) Acute

b) Right

c) Obtuse

CountdownCountdown

10

Classify this angle:

a) Acute

b) Right

c) Obtuse

CountdownCountdown

10

What we already know about triangles:

• A triangle is a figure with three sides and three angles.

• The symbol for triangle is

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.

Triangles can be classified by the measures of their angles.

• An acute triangle has three acute angles.

• An obtuse triangle has one obtuse angle.

• A right triangle has one right angle.

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

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

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

• An isosceles triangle has at least two congruent sides.

• An equilateral triangle has all three sides congruent.

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

CountdownCountdown

10

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 / ScaleneCountdownCountdown

10

Classify this triangle by angles and by sides

1. Acute / Isosceles

2. Obtuse / Isosceles

3. Acute / Scalene

4. Obtuse / Scalene

614

18

130

3515

CountdownCountdown

10

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 / ScaleneCountdownCountdown

10

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.

Independent Practice

Independent Practice

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

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.

References

Glencoe McGraw-Hill Math Connects Course 2, Study Guide and Intervention

and Practice Workbook, 2008.

Wiens, James, Classifying Triangles, PowerPoint presentation, November 2008.