The area of regular polygons is used to measure the region covered by the polygon in two-dimensional space. Since it is a two-dimensional region, we use square units to measure the area. The area of a regular polygon can be calculated using the length of its apothem and the length of one of its sides. However, it is also possible to calculate the area of regular polygons by simply using the length of one of their sides.

Here, we will learn about the formulas that we can use to calculate the area of these polygons. Then, we will apply these formulas to solve some problems.

GEOMETRY
formula for the area of a hexagon

Relevant for

Learning about the area of regular polygons with examples.

See formulas

GEOMETRY
formula for the area of a hexagon

Relevant for

Learning about the area of regular polygons with examples.

See formulas

Calculate the area of regular polygons using the apothem and sides

The area of any regular polygon can be calculated using the length of its apothem and the length of one of its sides. The area formula in these cases is:

A=\frac{1}{2}nal

where a is the length of the apothem, l is the length of one of the sides and n is the number of sides of the polygon.

This formula is derived from the fact that we can divide any regular polygon into triangles. For example, consider the following regular hexagon:

hexagon divided into six triangles with apothem

We can divide this hexagon into six congruent triangles. We know that the area of a triangle is equal to one-half of its base multiplied by its height. In this case, the height of the triangle is the apothem and the base is equal to one of the sides of the hexagon. Therefore, the area of each triangle is:

A_{t}=\frac{1}{2}al

Now, we see that we have six of these triangles (which is equal to the number of sides of the hexagon). Therefore, the area of the hexagon is:

A=\frac{1}{2}(6)al

A=3al


Calculate the area of regular polygons using only the sides

The area of regular polygons can also be calculated using only the length of one of their sides. To achieve this, we can use the area formula that we saw earlier. However, we need to find an expression for the apothem in terms of its sides. An expression can be found using trigonometry.

We can use the tangent function to find the apothem. Therefore, the resulting formula is the following:

A=\frac{{{a}^2}n}{4\tan(\frac{180}{n})}

where a is the length of one of the sides of the polygon and n is the number of sides.


Area of regular polygons – Examples with answers

The areas of the following regular polygons are found using the formulas seen above. Each example has its respective solution, where you can observe the process used.

EXAMPLE 1

If a pentagon has sides of length 8 m and an apothem of 5.5 m, what is its area?

A pentagon is a regular polygon with five sides. We use the area formula for regular polygons with the lengths l = 8 and a = 5.5. Therefore, we have:

A=\frac{1}{2}nla

A=\frac{1}{2}(5)(8)(5.5)

A=110

So the area of the pentagon is 110 m².

EXAMPLE 2

What is the area of a heptagon that has sides of length 8 m and an apothem of 8.3 m?

The heptagon is a seven-sided regular polygon, so we have n = 7. Furthermore, we have the lengths l = 8 and a = 8.3. Therefore, using the area formula with these values, we have:

A=\frac{1}{2}nla

A=\frac{1}{2}(7)(8)(8.3)

A=232.4

Thus, the area of the heptagon is 232.4 m².

EXAMPLE 3

Determine the area of a hexagon that has sides of 10 m.

The hexagon is a six-sided regular polygon, so we have n = 6. In this case, we only have the length l = 10. Therefore, using the second area formula:

A=\frac{{{l}^2}n}{4\tan(\frac{180}{n})}

A=\frac{{{(10)}^2}(6)}{4\tan(\frac{180}{6})}

A=\frac{600}{4\tan(30)}

A=\frac{600}{2.31}

A=259.7

Thus, the area of the hexagon is 259.7 m².

EXAMPLE 4

If an octagon has sides of length 5 m, what is its area?

The octagon is an eight-sided regular polygon, so we have n = 8. Similar to the previous exercise, we only have the length l = 5. Therefore, we use these values in the second formula for the area:

A=\frac{{{l}^2}n}{4\tan(\frac{180}{n})}

A=\frac{{{(5)}^2}(8)}{4\tan(\frac{180}{8})}

A=\frac{200}{4\tan(22.5)}

A=\frac{200}{1.66}

A=120.5

Thus, the area of the octagon is 120.5 m².


Area of regular polygons – Practice problems

Apply the formulas for the volume of three-dimensional figures to solve the following practice problems. Select an answer and click “Check” to check that you got the correct answer.

What is the area of a pentagon that has sides of length 9m and an apothem of 6.2m?

Choose an answer






What is the area of a hexagon that has sides of length 6m and an apothem of 5.2m?

Choose an answer






If a heptagon has sides of 8m, what is its area?

Choose an answer






What is the area of an octagon that has sides of 9m?

Choose an answer







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