Lesson 7ª

PERIMETER OF A REGULAR PENTAGON

WE call perimeter to the outer edges of a shape and since the edges of a regular pentagon are 5 equal segments, its perimeter will be the sum of all its sides. Thus, we can say that the area of a pentagon is equal to the perimeter times the apothem divided by two.

15(2).20   The perimeter of a pentagon measures 25 cm. and its area equals 50 cm2. What is the length of its apothem?

CALCULATING THE AREA OF A REGULAR HEXAGON

First, draw a regular hexagon.

As you can see, there are 6 equilateral triangles (equal sides, equal angles).

We can use the same method used to calculate the area of a regular pentagon to calculate the area of a hexagon.

1st Calculate the area of a triangle multiplying its height (or the apothem of the regular hexagon) by its base (or side of the hexagon). Divide this product by 2 and multiply this result by 6 (number of sides in a hexagon or number of triangles):

We solve the area of the 6 triangles (shown in the following image):

2nd Consider the hexagon as a single triangle whose base is the perimeter of the hexagon, in other words, the sum of the bases of the 6 triangles and their height (or apothem):

As you can see, both methods lead to the same result. Choose whichever you like.

15(2).21   How many square metres does a hexagonal park (filled with trees) have? The measurements are in the following image: