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4-6
Unions and Basic Geometric Shapes
Objectives:
1. draw and identify basic figures of geometry and polygons
2. identify statements as sometimes, always, or never
3. apply definition of polygon to various figures
Big Idea: Some unions of rays are angles; some unions of
segments are polygons.
Draw a union of two rays that is not an angle.
Draw the union of 3 segments that is not a triangle.
Draw the union of 4 segments that is not a quadrilateral.
Angle – union of two rays with the same endpoint. Named
EHR, RHE, or H
Sides of angle – rays that make up the angle
HE and HR
Vertex of angle – common endpoint of two rays.

Math History – Ancient Babylonians told us that a full circle is 360
based on the fact that stars move a full circle in 365 days (1 year)
but 365 not as easy to work with as 360.
Protractor – instrument used to measure angles
Baseline – line segment from 0 to 180.
Acute angle – measures 0  x < 90
Right angle – x = 90
Obtuse angle – measures 90 < x < 180
Straight angle – x = 180
Collinear – 3 points that lie on the same line.
no
Polygon – a union of segments in which each segment intersects
exactly two others, one at each of its endpoints.
 Encloses a single region in a plane
yes
no
no
Polygons have a fixed number of sides and # of sides = # of
angles
3 sides = triangle
7 sides = heptagon
4 sides =
8 sides = octagon
quadrilateral
9 sides = nonagon
5 sides = pentagon
10 sides = decagon
6 sides = hexagon
n sides = n-gon
To name a figure, start at any vertex and name all letters
clockwise or counter-clockwise until back to the starting letter.
Triangle is the only one with a symbol in the front.
Classify – give type of polygon
Name – give specific name of that polygon. (using letters)