Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
3. Areas of Polygons
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Exercise 22 Page 614

Find the perimeter and the apothem. Then substitute their values in the formula A= 12aP to find the area of the regular polygon.

127.31units^2

Practice makes perfect

The area of a regular polygon is half the product of the apothem and the perimeter. Note that we are only given the side length.

We will first need to find the perimeter and the apothem of the polygon. Then we will use the formula A= 12aP to find the area.

Finding the Perimeter

Since we have a regular hexagon whose side length is 7units, we can find the perimeter by multiplying 6 by 7. 6* 7= 42units

The perimeter of the given polygon is 42units.

Finding the Apothem

Let's now find the apothem. To do so, we will start by drawing the radii of the hexagon. Be aware that the radii divide a regular hexagon into six congruent isosceles triangles.

Since corresponding angles of congruent figures are congruent, the vertex angles of the isosceles triangles formed by the radii are congruent. Moreover, since a full turn measures 360^(∘), we can divide 360 by 6 to obtain their measures. 360/6=60^(∘) The vertex angles of the isosceles triangles measure 60^(∘) each.

The apothem bisects both the vertex angle of the isosceles triangle and the opposite side of the vertex, which is a side of the hexagon. As a result, a 30^(∘)-60^(∘)-90^(∘) triangle is created. The length of its shorter leg is 7÷ 2=3.5units.

In this type of special triangle the length of the longer leg, which is the apothem, is sqrt(3) times the length of the shorter leg. Longer Leg: sqrt(3)* 3.5=3.5sqrt(3)units Therefore, the length of the apothem is 3.5sqrt(3)units.

Finding the Area

To find the area of the given regular polygon, we will substitute a=3.5sqrt(3) and P= 42 in the formula A= 12aP.
A=1/2aP
A=1/2(3.5sqrt(3))( 42)
Evaluate right-hand side
A=1/2(147sqrt(3))
A=147sqrt(3)/2
A=127.30573...
A≈ 127.31
The area of the given regular polygon is approximately 127.31units^2.