Learn to identify and name polygons'

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Learn to identify and name polygons.
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Vocabulary
polygon side vertex of a polygon regular polygon
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Triangles and rectangles are examples of
polygons. A polygon is a closed plane figure
formed by three or more line segments. Each line
segment forms a side of the polygon, and meets,
but does not cross, another line segment at a
common point. This common point is a vertex of a
polygon.
The polygon at left has six sides and
six vertices.
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Additional Example 1A 1B Identifying Polygons
Determine whether each figure is a polygon. If it
is not, explain why not.
A.
B.
The figure is a polygon. It is a closed figure
with 4 line segments.
The figure is not a polygon. It is not a closed
figure.
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Additional Example 1C 1D Identifying Polygons
Determine whether each figure is a polygon. If it
is not, explain why not.
C.
D.
The figure is not a polygon. The figure is not
formed by line segments.
The figure is not a polygon. There are line
segments in the figure that cross.
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Try This Example 1A 1B
Determine whether each figure is a polygon. If it
is not, explain why not.
A.
B.
The figure is a polygon. It is a closed figure
with 5 line segments.
The figure is not a polygon. It is not a closed
figure.
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Try This Example 1C 1D
Determine whether each figure is a polygon. If it
is not, explain why not.
C.
D.
The figure is not a polygon. The figure is not
formed by line segments.
The figure is not a polygon. There are line
segments in the figure that cross.
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Polygons are classified by the number of
sides and angles they have.
Triangle 3 sides 3 angles
Quadrilateral 4 sides 4 angles
Pentagon 5 sides 5 angles
Hexagon 6 sides 6 angles
Heptagon 7 sides 7 angles
Octagon 8 sides 8 angles
Nonagon 9 sides 9 angles
Decagon 10 sides 10 angles
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Additional Example 2 Classifying Polygons
Name each polygon.
A.
B.
Octagon
Quadrilateral
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Try This Example 2
Name each polygon.
B.
A.
Quadrilateral
Pentagon
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A regular polygon is a polygon in which all sides
are congruent and all angles are congruent.
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Additional Example 3 Identifying and Classifying
Regular Polygons
Name each polygon and tell whether it is
a regular polygon. If it is not, explain why not.
B.
A.
The figure is a quadrilateral. It is not a
regular polygon because all of the sides are not
congruent.
The figure is a regular quadrilateral. A regular
quadrilateral is also called a square.
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Try This Example 3
Name each polygon and tell whether it is
a regular polygon. If it is not, explain why not.
B.
A.
The figure is a triangle. It is not a regular
polygon because all sides and angles are not
congruent.
The figure is a regular triangle.
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Lesson Quiz
Determine whether each statement is true or
false. 1. Every polygon is a closed figure. 2.
Every open figure is a polygon. 3. A pentagon
with sides lengths of 10 units and angles
measuring 108 is a regular polygon. 4. A
quadrilateral with side lengths of 10, 12, 10,
and 12 units is a regular polygon. 5. What is the
name of a five-sided polygon?
true
false
true
false
pentagon