Pentagon Shape
A pentagon shape is a flat shape or a flat (two-dimensional) 5-sided geometric shape. In geometry, it is considered as a is a five-sided polygon with five straight sides and five interior angles, which add up to 540°. Pentagons can be simple or self-intersecting. A simple pentagon (5-gon) must have five straight sides that meet to create five vertices but do not intersect with each other. A self-intersecting regular pentagon is called a pentagram.
What Is a Pentagon?
A pentagon is a geometric two-dimensional shape with five sides and five angles. The definition of pentagon shape is derived from the Greek word as “Penta” denotes five, and “gon” denotes angle. The pentagon is a 5-sided polygon. The home plate seen on a baseball field is an example of a pentagon shape.
Formula of Pentagon
Formulas of the pentagon help us to find out everything about a pentagon shape. From the general formula of polygons, we get the following formula of the pentagons.
- Diagonals of a pentagon: = n × (n − 3) ÷ 2 = 5 × (5 − 3) ÷ 2 = 5
- Sum of interior angles of a pentagon: = 180° × (n − 2) = 180° × (5 − 2) = 540°
- Exterior angle of Pentagon: = 540° ÷ n = 540° ÷ 5 = 108°
- Interior angle of Pentagon: = 360° ÷ n = 360° ÷ 5 = 72°
- Area of the Pentagon = 1/2 × Perimeter × Apothem sq units
- Perimeter of a Pentagon = (side1 + side2 +side3 + side4 + side5) units
Pentagon Properties
A pentagon has five straight sides that do not overlap. If the five sides of a shape are not connected, or one side of the shape is curved, then this is not a pentagon. According to the Pentagon's definition, a pentagon has 5 angles.
| Properties of Pentagon Shape | The Formula of Pentagon Shape |
|---|---|
| Sides = 5 | n = 5 |
| Diagonals = 5 | n × (n − 3) ÷ 2 |
| Interior angle = 72° | 360° ÷ n |
| Exterior angle = 108° | 540° ÷ n |
| Area of pentagon | 1/2 × Perimeter × Apothem sq units. |
| Perimeter of pentagon | s1 + s2 + s3 + s4 + s5 units |
Pentagon Shape Examples
There are a lot of Pentagon-shaped objects that we go through in our daily lives. Given below are regular and irregular pentagon shape examples. You'll learn more interesting Pentagon-shaped facts if you look at Pentagon-shaped examples such as okra, symmetrical starfish, and other such objects.
Can you classify these pentagon shape objects and identify the pentagon shape facts?
Pentagon Shape Facts
- The Pentagon is the headquarters of the United States Department of Defense in Washington DC, an example of a typical Pentagon shape.
- President Roosevelt decided that a new building for the Department of War was needed during World War II.
- The interesting features of the Pentagon shape were that the architect chose the Pentagon shape for the building, which reduced the distance that people had to walk from one office to another.
Area of Pentagon
The area of the Pentagon is the area occupied within its 5 sides. To find the area, we need to know what kind of pentagon we have and what information we know about our pentagon. A regular Pentagon can be divided into 5 triangles.
Area of the pentagon = 5 × Area of the triangle
Area of the Pentagon = 1/2 × Perimeter × Apothem sq units
Apothem is a line drawn from the center of a polygon, perpendicular to one of its sides. It’s also called the radius of the pentagon.
Area of a Pentagon Calculation
Consider triangle POQ, in which, OA = apothem and OA perpendicular to PQ. Suppose the length of the side is 6 inches. Consider the right triangle POA. OP = hypotenuse and AP = 1/2 of pentagon's side = 3 inches
∠AOP = 36° (∵ 72° ÷ 2)
∠OPA = 54° (∵ 108° ÷ 2)
Tangent of an angle
tan 36° = opposite/adjacent
= opposite/apothem
= 3/apothem
Apothem = 3/tan 36°
= 3/0.72
= 4.16 inches
Area = 1/2 × 5 × side × apothem
= 1/2 × perimeter × apothem
= 1/2 × 30 × 4.16
= 15 × 4.16
= 62.4 sq in
Thinking Out Of the Box!
- A pentagram is a star shape obtained from the five diagonals of a regular pentagon. Is it true?
- How many triangles could be there in such a pentagon with 5 diagonals? Can it really be 35?
Perimeter of Pentagon
The perimeter of a regular or irregular pentagon is the distance around its five sides. Thus, it is the sum of its sides.
Perimeter of a Pentagon = (side1 + side2 +side3 + side4 + side5) units
If all sides of the regular Pentagon have the same measures, The Perimeter of a regular pentagon = 5 × side units
If each side measures 6.3 feet, the perimeter of the pentagon = 5 × 6.3 = 31.5 feet
Difference Between Regular and Irregular Pentagons
Based on angle measures and Pentagon sides, it is categorized into regular and irregular Pentagon, Convex, and Concave Pentagon. The table shows the difference between the pentagons.
| Regular pentagon | Irregular pentagon |
| All the interior angles and the sides are equal | All the interior angles and the sides are of different measures |
| Convex pentagon | Concave pentagon |
| All the interior angles are < 180°, and the vertices point outwards | One or more interior angles are > 180°, and the vertices point inwards |
Look at the image below to visualize regular and irregular pentagons along with two other types of pentagons - concave and convex pentagons.
Important Notes on Pentagon Shape
- A regular pentagon has 10 isosceles right triangles.
- If the length of a side and the apothem are given, calculate area = 1/2 × Perimeter × Apothem sq units.
- If given the length of one side, find the apothem and then the area of the pentagon.
- Apothem = side/2 ÷ tan36°.
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FAQs on Pentagon
What is Pentagon Shape in Geometry?
A two-dimensional shape with 5 sides is known as a pentagon. In other words, we call it a 5-sided polygon.
What Is the 5 Sided Shape Called?
A five-sided shape is called a pentagon. If all five sides are equal then we call it a regular pentagon, whereas if any two of the sides are different in measurement, we call it an irregular pentagon. On the other hand, a six-sided shape is a hexagon, and an octagon has eight sides.
Is a Pentagon a Parallelogram?
No, a pentagon is not a parallelogram, it is a five-sided polygon. A parallelogram has only four sides.
What is Similarity Between a Quadrilateral and a Pentagon Shape?
A quadrilateral and a pentagon both are closed polygons with the sum of their exterior angles equal 360°.
Does a Pentagon Have Symmetry?
A regular pentagon has 5 lines of symmetry. There is no line of symmetry for an irregular pentagon.
What Is the Largest Number of Parallel Sides in a Pentagon?
A regular Pentagon will have 0 parallel lines, but an irregular Pentagon can have 2 (1 pair) or 4 (2 pairs) parallel lines.
How Many Angles Are in a Pentagon?
A pentagon has five angles. In the case of a regular pentagon, each of these five interior angles measures 72º each.
What Is the Sum of Interior Angles of the Pentagon?
The sum of all five interior angles of a pentagon is 540°.
How Many Lines of Symmetry Does a Pentagon Shape Have?
A regular pentagon shape has 5 lines of symmetry.
What Is the Exterior Angle of the Pentagon?
The measurement of the exterior angle of the pentagon is 108°.