Angles and Triangles

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Angles and Triangles

• Terry Scates
• Newton, Kansas

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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.)

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Instructor Notes

• 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.)

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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

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What we already know about angles

• An angle has two sides that share a common
  endpoint.

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What we need to know about angles

• The point where the sides meet is called the
  vertex.

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What we need to know about angles

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

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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

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Right Angle

• Find some examples of right angles in the
  classroom

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Acute Angle

• Find some examples of acute angles in the
  classroom

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Obtuse Angle

• Find some examples of obtuse angles in the
  classroom

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Classify this angle
Classify this angle

1. Acute
2. Right
3. Obtuse

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Classify this angle

1. Acute
2. Right
3. Obtuse

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Classify this angle

1. Acute
2. Right
3. Obtuse

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What we already know about triangles

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

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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.

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Triangles can be classified by the measures of
their angles.
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• An acute triangle has three acute angles.

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• An obtuse triangle has one obtuse angle.

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• A right triangle has one right angle.

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Triangles can also be classified by the lengths
of their sides.
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• Sides that are the same length are congruent
  segments and are often marked by tick marks.

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

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• An isosceles triangle has at least two congruent
  sides.

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• An equilateral triangle has all three sides
  congruent.

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Classify this triangle by angles and by sides
7
70
4
40
70
7

1. Acute / Isosceles
2. Obtuse / Isosceles
3. Acute / Scalene
4. Obtuse / Scalene

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Classify this triangle by angles and by sides
8
90
30
4
9
60

1. Acute / Isosceles
2. Right / Isosceles
3. Acute / Scalene
4. Right / Scalene

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Classify this triangle by angles and by sides
14
130
6
15
35
18

1. Acute / Isosceles
2. Obtuse / Isosceles
3. Acute / Scalene
4. Obtuse / Scalene

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Classify this triangle by angles and by sides
7
60
60
7
7
60

1. Acute / Isosceles
2. Right / Isosceles
3. Acute / Equilateral
4. Obtuse / Scalene

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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.

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Independent Practice
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Independent Practice
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Answer Key for Independent Practice

• Obtuse / Isosceles
• Acute / Equilateral
• Right / Isosceles
• Acute / Isosceles

1. Obtuse / Isosceles
2. Acute / Equilateral
3. Obtuse / Scalene
4. Right / Scalene

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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.

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References

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