Classifying triangles

Classifying triangles

Written by: James WiensNewton, 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.

• 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.

Instructor Notes

Lesson Outline

I. Warm-up: Angle classificationII. Setting the Stage: III. Guided practice:

Turning Point QuestionsIV. Independent practice: Paper & pencilV. Closure: Write about triangles

Classify this angle:

a) Acuteb) Rightc) Obtuse

Classify this angle:

Classify this angle:

a) Acuteb) Rightc) Obtuse

Classify this angle:

a) Acuteb) Rightc) Obtuse

Classify by Angles• Key concept: Classify the triangle by

it’s largest angle. • If the largest angle is acute, then the

triangle is Acute. • If the largest angle is right, then the

triangle is Right. • If the largest angle is obtuse, then the

triangle is Obtuse.

Classify by Sides• Key concept: Measure the length of

each side. • If all three sides are the same length, then

the triangle is Equilateral. • If all two sides are the same length, then

the triangle is Isosceles.• If all three sides are a different length, then

the triangle is Scalene.

Setting the Stage• A piece of paper is cut

diagonally from corner to corner to form a triangle.

• What kind of triangle is formed based on the length of it’s sides?

Answer

Scalene

Setting the Stage

• A piece of paper is cut diagonally from corner to corner to form a triangle.

• What kind of triangle is formed based on the angles formed?

Answer

Acute

Classify this triangle by angles and by sides

1. Acute / Isosceles2. Obtuse / Isosceles3. Acute / Scalene4. Obtuse / Scalene

4

7

7

70

70

40

Classify this triangle by angles and by sides

4

8

90

60

30

9

1. Acute / Isosceles2. Right / Isosceles3. Acute / Scalene4. Right / Scalene

Classify this triangle by angles and by sides

1. Acute / Isosceles2. Obtuse / Isosceles3. Acute / Scalene4. Obtuse / Scalene

614

18

130

3515

Classify this triangle by angles and by sides

7

7

7

60

60

60

1. Acute / Isosceles2. Right / Isosceles3. Acute / Equilateral4. Obtuse / Scalene

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 it possible for an obtuse triangle to also be equilateral? Explain why or why not.

References

• All content of lesson designed and written by James Wiens, 7th grade math teacher, Newton Kansas.