Perimeter of Regular Polygons with Sample Problems

Contributed by:
Diego
This pdf contains:-
Regular Pentagon
Regular Hexagon
Regular Octagon
In Euclidean geometry, a regular polygon is a polygon that is equiangular and equilateral. Regular polygons may be either convex or star.
1. Lesson Notes
The Perimeter of a Regular Polygon
This section will focus on how to calculate Regular Pentagon
the Perimeter of a Regular Polygon.
We recall that a polygon is regular if all of
its sides are congruent and if all its interior
angles are congruent.
Remember that congruent means identical.
The regular polygons that we will focus on in
this section are: # of sides(n) = 5
Equilateral Triangle Regular Hexagon
# of sides(n) = 3
Square
# of sides(n) = 6
Regular Octagon
# of sides(n) = 4
# of sides(n) = 8
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2. Lesson Notes
Regular Decagon P = ( n )( b )
Finally, we calculate the perimeter (P).
P = ( n )( b )
P = (10 )( 3cm )
P = 30cm
So, the perimeter of the regular decagon is
# of sides(n) = 10 30cm.
Let’s try a different type of question where
In order to calculate the perimeter of any we are given the perimeter of a regular
of the regular polygons, we will use the polygon and we want to calculate the length
formula: of one of its sides.
P = ( n )( b ) The perimeter of the regular pentagon given
below is 35cm. Determine the value of x.
“P” is the Perimeter
“n” is the number of sides
“b” is the side length
Let’s try an example using this formula.
Calculate the perimeter of the regular
decagon given below.
First, we state the information that we know
about the regular pentagon.
P = 35cm n = 5 b=x
Next, we state the formula to calculate the
perimeter (P) of a regular pentagon.
P = ( n )( b )
First, we state the information that we know
about the regular decagon.
b = 3cm n = 10
Next, we state the formula to calculate the
perimeter (P) of a regular decagon.
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3. Lesson Notes
Finally, we calculate the value of x. Example
P = ( n )( b )
1. Calculate the perimeter of the
35cm = ( 5 )( x ) equilateral triangle below.
35cm ( 5 )( x )
=
5 5
7cm =
( 5 )( x )
5
x = 7cm
Step 1: Statebthe
= 7cm
information you know
So, all of the sides of the regular pentagon about the triangle.
measure 7cm in length. n=3
b = 7cm
We are ready to do more challenging P = ( n )( b )
examples. n=3
P the
Step 2: State ( )( )
n b to calculate
= formula
b = 7cm
the perimeter (P) of an equilateral
triangle. n=3
P = ( n )( b )
Step 3: Calculate the perimeter (P).
P = ( n )( b )
P = ( 3)( 7cm )
P = 21cm
So, the perimeter of the equilateral
triangle is 21cm.
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4. Lesson Notes
2. The perimeter of the square given below 3. Calculate the perimeter of the regular
is 24cm. Determine the value of x. pentagon given below.
P = 24cm Step 1: Statenthe
=5 information you know
Step 1: State the information you know
about the pentagon.
n=4
about the square. b = 3cm
b P= =x 24cm Pn==(5n )( b )
P =n (=n4)( b ) b = 3cm
n=5
b=x
P = 24cm P the
Step 2: State ( )( )
n b to calculate
= formula
Step 2: State the(formula
Pn == 4n )( b ) to calculate the perimeterb(P)
= 3cm
of a regular pentagon.
the perimeterb(P)
= xof a square. P = ( n )( b )
P = ( n )( b )
Step 3: Calculate the perimeter (P).
Step 3: Calculate the value of x. P = ( n )( b )
P = ( n )( b ) P = ( 5 )( 3cm )
24cm = ( 4 )( x ) P = 15cm
24cm ( 4 )( x ) So, the perimeter of the regular
= pentagon is 15cm.
4 4
6cm =
( 4 )( x )
4
x = 6cm
The value of x is 6cm.
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5. Lesson Notes
4. The perimeter of the regular hexagon 5. A regular octagon has a side length of
given below is 72cm. Determine the 11cm. Calculate the octagon’s perimeter.
value of x.
Step 1: State the information you know
about the octagon.
b = 11cm n=8
Step 2: State the formula to calculate
the perimeter of a regular octagon.
P = ( n )( b )
Step 3: Calculate the perimeter (P).
P = 72cm P = ( n )( b )
Step 1: State the information you know
n=6
about the hexagon.
P = ( 8 )(11cm )
b=x P = 88cm
P = 72cm
P =n(=n )(
6 b) So, the perimeter of the regular octagon
b=x is 88cm.
P = 72cm
Pn==(6n )( b )
Step 2: State the formula to calculate
the perimeterbof=axregular hexagon.
P = ( n )( b )
Step 3: Calculate the value of x.
P = ( n )( b )
72cm = ( 6 )( x )
72cm ( 6 )( x )
=
6 6
12cm =
( 6 )( x )
6
x = 12cm
The value of x is 12cm.
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