Classifying Triangles

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Transcript Classifying Triangles

Angles and Triangles
Terry Scates
Newton, Kansas
Instructor Notes
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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.)
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.)
Lesson Outline
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Warm-up: Angle classification
Setting the Stage:
Guided practice:
Turning Point Questions
Independent practice: Paper & pencil
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 Angle
Find some examples of obtuse angles in the classroom:
Classify this angle:
Classify this angle:
a) Acute
b) Right
c) Obtuse
10
Countdown
Classify this angle:
a) Acute
b) Right
c) Obtuse
10
Countdown
Classify this angle:
a) Acute
b) Right
c) Obtuse
10
Countdown
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
70
7
4
40
70
1.
2.
3.
4.
7
Acute / Isosceles
Obtuse / Isosceles
Acute / Scalene
Obtuse / Scalene
10
Countdown
Classify this triangle
by angles and by sides
8
90
30
4
9
60
1.
2.
3.
4.
Acute / Isosceles
Right / Isosceles
Acute / Scalene
Right / Scalene
10
Countdown
Classify this triangle
by angles and by sides
6
14
130
15
35
18
1.
2.
3.
4.
Acute / Isosceles
Obtuse / Isosceles
Acute / Scalene
Obtuse / Scalene
10
Countdown
Classify this triangle
by angles and by sides
7
60
60
7
7
60
1.
2.
3.
4.
Acute / Isosceles
Right / Isosceles
Acute / Equilateral
Obtuse / Scalene
10
Countdown
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
E. Obtuse / Isosceles
B. Acute / Equilateral
F. Acute / Equilateral
C. Right / Isosceles
G. Obtuse / Scalene
D. Acute / Isosceles
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.