Post on 31-Dec-2015
transcript
Bell Work:
Describe each angle as acute, obtuse or straight and then name each angle.
Answer:
<ABD is Obtuse
<ABC is Acute
<CBD is Acute
Lesson 19:Polygons
Polygons*: closed plane figures with straight sides. They have the same number of sides and angles.
Example:
Which of these figures is a polygon?
Answer:
No: This figure is closed but it is curved.
No: This figure is not closed.
No: This figure is not a plane figure.
Yes: Closed figure with straight lines.
Regular Polygon*: All sides are the same length and all angles are the same size.
Example:
Which polygon is not regular?
A B C D
Answer:
Figure D
Polygons are named by the number of their sides and angles.
Name of Polygon
Number of Sides
Name of Polygon
Number of sides
Triangle 3 Octagon 8
Quadrilateral
4 Nonagon 9
Pentagon 5 Decagon 10
Hexagon 6 Hendecagon
11
Heptagon 7 Dodecagon 12
A polygon with more than 12 sides may be referred to as an n-gon, with n being the number of sides.
Thus, a polygon with 15 sides is a 15-gon.
Vertex*: The point where two sides of a polygon meet.
(plural: vertices)
A particular polygon can be identified by naming the letters of its vertices in order. We may name any letter first. The rest of the letters can be named clockwise or counterclockwise.
Example:
What are some possible names for the polygon below?
How many did you come up with?
U
S
V T
Answer:
8 possible names
USTV, UVTX, STVU, SUVT, TSUV, TVUS, VTSU, VUST
Congruent*: Having the same size and shape.
Orientation does not have to be the same
These figures are not congruent because they are not the same size, but they are similar because they have the same shape.
The second figure is a dilation (enlargement) of the first figure meaning we could use a magnifying glass to enlarge the first figure to equal the second figure.
Practice:
Which triangles appear to be similar?
A B C D
Answer:
Triangles A, B and C are similar
Practice:
Which triangles appear to be congruent?
Answer:
Triangles A and C are congruent.
HW: Lesson 19 #1-30
Due Tomorrow