Perimeter of a Polygon
I. Learning Objectives
Cognitive: 1. Derive a formula for finding the perimeter of a polygon
2. Find the perimeter of a polygon
Psychomotor: Measure the perimeter of a polygon
Affective: Show accuracy in measuring
II. Learning Content
Skills: 1. Deriving a formula for finding the perimeter of a polygon
2. Finding the perimeter of a polygon
Refence: BEC-PELC IV.A. 1.2
Materials: textbook, real objects, diagrams, illustrations, cut outs of polygons, meter
stick, tape measure
III. Learning Experience
A. Preparatory Activities
Identifying polygons by means of a guessing game
Example: I am polygon with four equal sides. Who am I?
Ask what unit of measure is appropriate for objects such as these:
● distance between buildings
● sides of a handkerchief
● safety pin
Show a plain handkerchief. Do you carry your handkerchiefs everyday? Why? What are
the uses of a handkerchief?
B. Developmental Activities
a. Show a piece of lace and a square hadnkerchief.
If I'm going to sew lace around my handkerchief would this lace be enough? Get the
children's opinion. What are we going to do to be sure on the length of the lace? Let the pupils
measure the sides and compute for the distance around. Ask what they measured and why. Tell
them to describe what they measured leading them to use the phrase distance around. Introduce
the term perimeter for this distance. Have the pupils illustrate the object (handkerchief) on the
board with the corresponding measures and ask one pupil to write the number sentence for this.
(25 + 25 + 25 + 25) or (4 x 25)
The formula in finding the perimeter of a square is S + S + S + S or P = 4 x S
b. Show a picture frame hanging in the classroom.
What is the shape of the picture frame? (rectangle)
Measure the sides of the frame. What can you say about the lenghts? Widths?
To find the perimeter, just add the sides.
The formula in finding the perimeter of a rectangle is L1 + W1 + L2 + W2 or
P = 2L + 2W or
P = 2 (L+W)
c. Show some polygons to be measured and have them compute the perimeter.
P=5+6+5+5+6+5 P = 3 + 15 + 3 + 5 + 7 + 5 + 7 + 5
= 32 cm = 50 cm
How do you measure the perimeter of the other polygons?
2. Fixing Skills
a. Find the perimeter of each figure. (See figure A on the other page.)
b. Group the pupils into 4 groups and have them find the perimeter of the following:
1) their classroom
2) a table top
3) a pupil's desk top
4) chalk board
In each case, they will have to decide on the appropriate unit or measurement.
What do you mean by the word appropriate? What is the other term for appropriate? Why
do we have to be accurate in measuring things?
What is perimeter?
How do you find the perimter of a polygon?
Give the formula for finding the perimeter of a square, rectangle, and the other polygons.
1. Have the pupils draw a rectangle.
Ask them to measure the perimeter and record it.
2. Let pupils draw the diagonal of the rectangle. Instruct them to
cut the rectangle along its diagonal and arrange the parts to form
3. Let them measure its perimeter and record. Discuss why the
perimeter is now bigger. (Longer sides are on the outside.)
4. Let the pupils rearrange the two triangles to form a
parallelogram. Have them measure its perimeter and compare
this width the first two perimeter.
A. Give the perimeter of each figure.
B. Find the perimeter. Use the formula.
Make cutouts of polygons. Write the measurement of each side. Solve for the perimeter.