The document describes a lesson plan for teaching students about the sum of interior angles in polygons. Students will use geometry sketchpad software to explore and discover that the sum of interior angles in a triangle is always 180 degrees. They will then systematically investigate quadrilaterals, pentagons, hexagons, and heptagons to determine the sum of interior angles for each polygon based on the number of sides. By recording their results, students should recognize the pattern that the sum is (n-2)*180, where n is the number of sides. They will also determine the angle measure of each interior angle in regular polygons. Finally, students will apply what they learned to solve the problem of determining the angle brackets needed for a 72-

1. Jimmy Clemson
Dr. Adu-Gyamfi
MATE 4001
Sum of Interior Angle of a Polygon
Statement of Mathematical Investigation: In this investigation the students will explore
the concept of an interior angle of a polygon and figure out the sum of the interior angles of
different sides of polygons and the angle measures of their regular polygons.
An auditorium manager is building an auditorium and needs to know what angle brackets he
needs for the junctions of the wall. His building is going to have 72 sides and it will be regular.
What angle brackets does he need?
Exploration: Start by constructing a triangle and measuring the interior angles and their sum.
Is this true of all triangles? Test it out.
A regular polygon is a polygon where all the angle measure and side lengths are the same.
Knowing that a regular triangle has to have equal angles, what angle does it have to be in order to make
it a regular polygon? 60 . How did you come up with that.
Make a chart that shows the number of sides and sum of the interior angles and the angle of a side of
the regular polygon for that many sides.
Now move up to quadrilaterals.

2. B
A
C
D
m
m
m
m
m
DAB = 142.57°
ABC = 45.85°
DCB = 127.52°
ADC = 44.07°
DAB + m ABC + m DCB + m ADC = 360.00°
Is this always the case? Test it out.

3. B
A
C
D
m
m
m
m
m
DAB = 139.57°
ABC = 7.60°
DCB = 127.52°
ADC = 4.46°
DAB + m ABC + m DCB + m ADC = 279.14°
Be Careful! Here it would seem that our quadrilateral would not fit our pattern but look what
happened to angle A. It switched from an interior angle to an exterior angle. If you made it add
the interior angle it would still add up to 360 .
What angle measure for each side would make a quadrilateral a regular quadrilateral? Use
what you learned about finding a regular triangle to help find the angle for a regular
quadrilateral.
Record your results in your chart and move onto a pentagon.

4. m
m
m
m
m
m
CDE = 72.82°
DEA = 121.71°
EAB = 83.96°
ABC = 127.09°
BCD = 134.42°
CDE + m EAB + m DEA + m ABC + m BCD = 540.00°
C
B
D
A
E
The sum of the interior angles of a pentagon adds up to 540 . Does this work for all pentagons?
What angle measure for each angle would make a pentagon a regular pentagon?
Record your results in the table. Move onto the hexagon.

5. B
A
C
m
m
m
m
m
m
m
FAB = 95.69°
D
ABC = 133.24°
BCD = 109.54°
CDE = 139.34°
F
DEF = 132.95°
EFA = 109.23°
E
FAB + m ABC + m BCD + m CDE + m DEF + m EFA = 720.00°
The sum of the interior angles of a hexagon are 720 . Find the individual angle measure for a
regular hexagon. Record this in your chart.
Make a heptagon. What do you notice about the sum of the interior angles of a heptagon?
B
A
C
m
m
m
m
m
m
m
m
GAB = 130.75°
ABC = 133.24°
D
BCD = 109.54° G
CDE = 139.34°
DEF = 132.95°
GFE = 148.26°
F
AGF = 105.91°
E
GAB + m ABC + m CDE + m BCD + m DEF + m GFE + m AGF = 900.00°

6. Thesum of the interior angles of a heptagon is 900 . Find the interior angle measure of a
heptagon.
The chart should look something like this:
Number of sides
3
4
5
6
7
Sum of the Measure of Interior
Angles
180
360
540
720
900
Angle measure of Regular
Polygon
60
90
108
120
128.57
What is the formula for coming up with the sum of the measure of the interior angles?
(n-2)*180
An auditorium manager is building an auditorium and needs to know what angle brackets he
needs for the junctions of the wall. His building is going to have 72 sides and it will be regular.
What angle brackets does he need?
Angle=
Angle=
Angle=175

7. IDP TPACK TEMPLATE (INSTRUCTIONAL DESIGN PROJECT TEMPLATE)
NAME: ______Jimmy Clemson______ DATE:_____11/17/13___________
Content.
Describe: content here.
(COMMON CORE STANDARDS)
CCSS.Math.Content.HSG-MG.A.3 Apply geometric methods to solve design
problems (e.g., designing an object or structure to satisfy physical constraints
or minimize cost; working with typographic grid systems based on ratios).★
Describe:Standards of mathematical Practice
CCSS.Math.Practice.MP1 Make sense of problems and persevere in
solving them.
CCSS.Math.Practice.MP3 Construct viable arguments and critique the
reasoning of others.
CCSS.Math.Practice.MP4 Model with mathematics.
CCSS.Math.Practice.MP5 Use appropriate tools strategically.
CCSS.Math.Practice.MP8 Look for and express regularity in repeated
reasoning.
Pedagogy. Pedagogy includes both
what the teacher does and what the
student does. It includes where, what,
and how learning takes place. It is
about what works best for a particular
content with the needs of the learner.
3.
Describe instructional strategy (method) appropriate for the content, the
learning environment, and students. This is what the teacher will plan and
implement.
This is a guided exploratory lesson. I will pose the question to them at the beginning
of class. Since they most likely won’t have an understanding of regular polygons, this
will lead to a discussion of regular polygons and their properties.
I will guide the students through the first shape, a triangle. Have them draw a triangle
of sketchpad and measure the interior angles of it. Once they figure out that all
triangles add up to 180 we can discuss a regular triangle.
2. Describe what learner will be able to do, say, write, calculate, or solve as the
learning objective. This is what the student does.
From there the student works through the rest of the shapes and figure out the sum of
their interior angles and the angle measure of the regular polygon.
The students will create a way to find the sum of the interior angles based on the
number of sides and be able to solve the initial problem.
3. Describe how creative thinking—or, critical thinking, --or innovative problem
solving is reflected in the content.
The students are not given the pattern for finding the sum of the interior angles, the
students have to recognize the pattern and figure that out for themselves.

8. Technology.
1. Describethe technology
GSP is a microworld geometry software. GSP allows students to manipulate all
kinds of geometry and algebra and explore to gain an understanding of
mathematical concepts.
2.
Describe how the technology enhances the lesson, transforms content,
and/or supports pedagogy.
The technology allows the students to efficiently find the sum of the interior angles
and see if it hold true for all polygons.
Without the use of sketchpad this lesson would be too long for one period and much
more inaccurate.
3. Describe how the technology affects student’s thinking processes.
The technology will let the students at first see that triangles are always 180, but
when they get to quadrilaterals they will be tricked into thinking that it doesn’t
work for all quadrilaterals by the way sketchpad will measure the angles but
once that point is clarified then they will see that it works for all.
Reflect—how did the lesson activity
fit the content? How did the
technology enhance both the content
and the lesson activity?
Reflection
The lesson fit the content area fairly well because the students will have to use
geometric principles to find the answer to a word problem.
The technology lets the students efficiently tally up the totals of the interior angles.
Without the technology the students would have a hard time accurately computing
the sum of the interior angles and therefore would have a hard time seeing the pattern
that arises if they do not have the correct sums.

9. Lesson Plan Template MATE 4001 (2013)
Title:Polygons
Subject Area: Math 2
Grade Level: 9-11
Concept/Topic to teach: Sum of the Interior Angles of a Polygon
Learning Objectives:
Content objectives (students will be able to……….)
Students should be able to figure out the sum of the interior angles of a polygon based on the number
of sides the polygon has and the angle measures of the regular polygon of that many sides.
Essential Question
Given a polygon with a certain amount of sides can you figure out the angle
measures of its regular polygon?
Standards addressed:
Common Core State Mathematics Standards:
o
CCSS.Math.Content.HSG-MG.A.3 Apply geometric methods to solve design problems
(e.g., designing an object or structure to satisfy physical constraints or minimize cost;
working with typographic grid systems based on ratios).★
Common Core State Mathematical Practice Standards:
CCSS.Math.Practice.MP1 Make sense of problems and persevere in solving them.
CCSS.Math.Practice.MP3 Construct viable arguments and critique the reasoning of others.
CCSS.Math.Practice.MP4 Model with mathematics.
CCSS.Math.Practice.MP5 Use appropriate tools strategically.
CCSS.Math.Practice.MP8 Look for and express regularity in repeated reasoning.
o

10. Technology Standards: Copy and paste from NCDPI
HS.TT.1.1
Use appropriate technology tools and other resources to access information
(multi-database search engines, online primary resources, virtual interviews
with content experts).
HS.TT.1.2
Use appropriate technology tools and other resources to organize information
(e.g. online note-taking tools, collaborative wikis).
Required Materials:
Computers
Sketchpad
Paper/pencil
Notes to the reader:
Write anything here that you think the reader needs to know before implementing this lesson. For
example, if you are assuming that the students have already experienced a particular topic this is the
place to note that.
Time: Assume 90 minutes ***
Time
Teacher Actions
Student Engagement
Before
Introduce problem, as students won’t know
what a regular polygon is talk about a
regular polygon and interior angles.
Take notes on regular polygons and interior
angles.
20
Guide students through triangle exploration
Explore triangles and record observations
and summarize what the students learn.
on interior angles.
Assist in construction if needed. Introduce
chart for students to put down observations
and results.
“You are to explore quadrilaterals,
pentagons, hexagons, and heptagons.
Record your results in the chart and write

11. any observations you have underneath the
chart.
45
Circulate room, probing students to keep
them in the right direction
Students will work through all of the shapes
mentioned above and explore sum of
interior angles and angles of regular
polygons.
Have students fill in chart up front. Go over
observations that students had about
exploration.
During
Students will present their findings to the
rest of the class.
Discuss how students found the angle of
each regular polygon.
After
15
What if I gave you a polygon with s number
of sides. How would I find the sum of the
interior angles.
Students will attempt to figure out the
formula for the sum of interior angles.
Show explanation for why that formula is.
Have students complete initial problem.
Answer initial question of the day.
*** Your lesson plan should ALL be included here (the reader shouldn’t have to go anywhere else to find
the plans.)The teacher should be able to read it chronologically. The only things to be included at the
end of the plan are supplemental artifacts (e.g. handouts, tech files, ppt). If you chose not to use the
table then the time, teacher actions and student actions should be clearly noted throughout your plan.
Make sure that your lesson is detailed enough that someone else could teach from it. This is
especially important during class discussion phases. For example, be sure to detail what the
teacher should be sure to bring out in a whole class discussion, including questions to push
students to build conceptual understanding, questions to assess student understanding, and
transitions between portions of your lesson.
If students are working in pairs / small groups this should be noted (including how the groups
are to be determined)
All tasks / examples should be worked out and included in the body of the lesson plan
All HW should be worked out

12. Reflection
This technology helped my understanding of this concept because I was able to
dynamically check whether it checks out for each situation. It allowed me to figure this stuff
out with relative ease. It will be the same for the students although it is tricky at some points
because if you measure the angles on the <180 side, if you move the polygon so that that
particular angle is >180 the angle it measure is on the outside of the polygon, not the interior
angle. It shows you on sketchpad but some people won’t notice it. That could lead to student
to thinking that their conjectures are incorrect even though they probably are since this
formula is true for all polygons even non-convex ones. This could be a tricky part of the lesson.