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Classifying Triangles
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Geometry
1
1/22/2017
Two Ways to Classify Triangles
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By Their Sides
By Their Angles
Geometry
2
1/22/2017
Classifying Triangles
By Their Sides
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Geometry
Scalene
Isosceles
Equilateral
3
1/22/2017
Scalene Triangles
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No sides are the same length
The smallest angle is across from the
smallest angle, the largest angle is across
from the largest side
∴ the angles will all be different
120°
11
15°
4
45°
15°
13
Geometry
4
1/22/2017
Isosceles Triangles
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At least two sides are the same length
For our class, to reduce confusion, when we
use the term “isosceles” to describe a triangle
– it will have only two equal sides
the congruent sides are called legs, and the
unequal side is called the base
the base angles opposite the legs are also
congruent
48°
11
11
66°
66°
9
Geometry
5
1/22/2017
Equilateral Triangles
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All sides are the same length
Also equiangular
The angles of all triangles add up to 180°
∴ angles of a equilateral triangle are 60°
60°
11
11
60°
Geometry
60°
11
6
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Classifying Triangles
By Their Angles
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Geometry
Acute
Obtuse
Right
Equiangular
7
1/22/2017
Acute Triangles
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Acute triangles have three acute angles
Acute means less than 90°
Geometry
8
1/22/2017
Right Triangles
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Right triangles have one right angle.
Right angles result from the intersection of
perpendicular lines, are 90°. Why can there
be only one?
Geometry
9
1/22/2017
Obtuse Triangles
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Obtuse triangles have one obtuse angle
Obtuse angles are greater than 90°.
Why can there be only one?
Geometry
10
1/22/2017
Classify this triangle.
Right Scalene
Geometry
11
1/22/2017
Classify this triangle.
Obtuse Isosceles
Geometry
12
1/22/2017
Classify this triangle.
Acute Scalene
Geometry
13
1/22/2017
Classify this triangle.
40°
70°
70°
Acute Isosceles
Geometry
14
1/22/2017
Classify this triangle.
Obtuse Scalene
Geometry
15
1/22/2017
Classify this triangle.
Right Isosceles
Geometry
16
1/22/2017