Download 3.9 Angles of polygons - Fort Thomas Independent Schools

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3.9 ANGLES OF POLYGONS
I can find the angle measurement sum for any
polygon.
MATH MESSAGE
1. Draw
a large triangle on the blank piece of
paper on your desk.
2. Use your protractor to measure each angle;
label each angle.
3. Add the measure of the angles and record the
sum on our line plot (draw an “X” above the sum
for your triangle).
TEAR THE THREE ANGLES OFF
OF YOUR TRIANGLE
Arrange your 3 angles next to each other so they
line up.
What type of angle have you created?
What does this show?
DRAW EXAMPLES OF
Polygons
Convex Polygons
Not Polygons
Concave (nonconvex) Polygons
JOURNAL PAGES 85-86
Groups of 4
Mrs. H. will assign your group “quadrangle” or “pentagon”
CLASS DATA (JOURNAL PAGES 87 &
88)
Quadrangles
Group
Group Median
Pentagon
Group
Group Median
**When drawing lines to divide a polygon into triangles, the lines must go from one vertex to
another; they cannot start or end in the middle of the polygon or between the endpoints of the line
segments.
DAY 2
DIVIDING POLYGONS INTO
TRIANGLES
Why do you think the measures increase by 180°?
How many degrees are in a triangle?
Quadrangles divide into _______ triangles.
2 x 180° = 360°
HOW MANY TRIANGLES CAN BE
DRAWN IN A PENTAGON?
3 x 180° = 540°
HOW MANY TRIANGLES CAN BE
DRAWN IN A HEXAGON?
4 x 180° = 720°
Conclusion: When you add another side to the figure, you are able to draw an additional
triangle in the figure, which adds 180°.
What do you notice about the relationship between the number of sides of the
polygon and the number of triangles that can be drawn in it?
The number of triangles inside the polygon is 2 less than the number of sides.
MATH JOURNAL PAGE 89
(AND MM 94)
Name
Triangle
Quadrilateral/Quadrangle
Pentagon
Hexagon
Heptagon
Octagon
Nonagon
Decagon
Dodecagon
Number
of sides
Equation
Total Degrees
CENTERS
Centers
1.
Math Journal pages
90-91; tessellations
website
2. MM 93 (Left)
HOMEWORK
Study Link 3.9