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Calculating the area of the polygon

Source: licencja: CC 0.

Obliczanie pól wielokątów

Learning objectives

  • You will get to know the method of calculating the areas of the polygons by dividing them into smaller polygons.

  • You will notice the relationships between the perimeter of the polygon and its area.

Learning effect

  • You will learn to calculate the areas of the polygons by dividing them into smaller polygons, whose areas are easy to calculate.

  • You will learn to notice the relationship between the perimeter of the polygon and its area.

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nagranie abstraktu

Recollect the formulae and the most important concepts useful when calculating the areas of polygons. The aim of the class – calculating the area of the polygonarea of the polygonarea of the polygon, which is neither a triangle nor a quadrangle.

Task 1
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nagranie abstraktu

Guess how to calculate the area of the polygonarea of the polygonarea of the polygon presented in the diagram. Write down your conclusion.

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Source: GroMar, licencja: CC BY 3.0.

Use the conclusion to solve the task.

Task 2
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nagranie abstraktu

A hexagon is made of two identical isosceles trapezoids. The altitudes of these trapezoids equal 10 cm, and their bases 25 cm and 15 cm. Calculate the area of this hexagon.

Task 3
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nagranie abstraktu

Observe the relationship between the perimeter of the polygonperimeter of the polygon perimeter of the polygon and its area. Write down your conclusion.

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Source: GroMar, licencja: CC BY 3.0.

Do the tasks using the information.

Task 4
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nagranie abstraktu

Draw any 3 polygonpolygonpolygon, not being rectangles, on a squared sheet of paper. Each of them should have the surface area of 18. Calculate the perimeter of each of them. Assume a side of the squaresquaresquare as your unit.

Will the perimeter of the polygonperimeter of the polygon perimeter of the polygon change when you change its shape, and the area will remain the same?

Task 5
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nagranie abstraktu

A diagonal divides a trapezoidtrapezoidtrapezoid into two triangles. The area of the bigger one is twice as big as the area of the smaller triangle. How many times is the area of the whole trapezoid larger than the area of the smaller triangle?

Task 6

An extra task:

The surface area of a rectangular stamp equals 12 cmIndeks górny 2. What are the dimensions of this stamp if its length is three times larger than its width?

Task 7
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nagranie abstraktu

Analyse the material presented in the applet. Observe the relationship between the area of the rectanglerectanglerectangle and its perimeter. Write down an appropriate conclusion.

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Aplet geogebra: Pole i obwód prostokąta. Poniżej znajduje się galeria będąca wersją alternatywną dla aplikacji.
Source: GroMar, licencja: CC BY 3.0.
Task 8
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nagranie abstraktu

Jurek wants to buy a rectangular garden plot, whose area equals 1000 mIndeks górny 2. He wants to surround it with the smallest possible amount of a wire fence. What dimensions should this plot have?

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nagranie abstraktu

Having finished all the tasks,  do the consolidation tasks. Formulate the conclusions that you should remember.

  • The polygons with the same perimeters may have different areas.

  • The squaresquaresquare has the smallest perimeter among all rectangles with equal areas.

Exercises

Exercise 1
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Wersja alternatywna ćwiczenia: A frame, whose width is 2 cm, was cut out of a rectangle with dimensions 14 cm by 8 cm. The area of the rectangle after cutting out the frame is equal Możliwe odpowiedzi: 1. 56 cm2, 2. 72 cm2, 3. 40 cm2, 4. 112 cm2
Source: GroMar, licencja: CC BY 3.0.
Exercise 2
  1. rectanglerectanglerectangle with the smallest possibile perimeter should be built with 36 identical squares. Draw such a rectangle and calculate its perimeter.

  2. A rectangle, whose length is 10 cm and the area is 40 cmIndeks górny 2 was cut along one of its sides into a square (the largest possible) and a rectangle. Calculate the perimeters of the obtained figures.

  3. In a triangle the length of one of its sides equals the altitude drawn to this side. The area of this triangle equals 8. Calculate the altitude of this triangle.

Exercise 3

Draw any nonagon (9 gon) on a squared piece of paper. Assume the side of the square as the unit.

Explain in English how to calculate the area of this polygonpolygonpolygon.

Exercise 4
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Wersja alternatywna ćwiczenia: Indicate which pairs of expressions or words are translated correctly. Możliwe odpowiedzi: 1. wielokąt - polygon, 2. pole wielokąta - area of the polygon, 3. obwód wielokąta - perimeter of the polygon, 4. prostokąt - rectangle, 5. kwadrat - trapezoid, 6. trapez - square
zadanie
Source: GroMar, licencja: CC BY 3.0.
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Interaktywna gra, polegająca na łączeniu wyrazów w pary w ciągu jednej minuty. Czas zaczyna upływać wraz z rozpoczęciem gry. Jeden ruch to odkrywanie najpierw jednej potem drugiej karty z wyrazem. Każdy wyraz jest odczytywany. Kolejny ruch to odkrywanie trzeciej i czwartej karty. W ten sposób odsłuchasz wszystkie wyrazy. Nawigacja z poziomu klawiatury za pomocą strzałek, odsłuchiwanie wyrazów enterem lub spacją. Znajdź wszystkie pary wyrazów.
Source: Zespół autorski Politechniki Łódzkiej, licencja: CC BY 3.0.

Glossary

area of the polygon
area of the polygon

pole wielokąta

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wymowa w języku angielskim: area of the polygon
perimeter of the polygon
perimeter of the polygon

obwód wielokąta

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wymowa w języku angielskim: perimeter of the polygon
polygon
polygon

wielokąt

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wymowa w języku angielskim: polygon
rectangle
rectangle

prostokąt

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wymowa w języku angielskim: rectangle
square
square

kwadrat

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wymowa w języku angielskim: square
trapezoid
trapezoid

trapez

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wymowa w języku angielskim: trapezoid

Keywords

area of the polygonarea of the polygonarea of the polygon

perimeter of the polygonperimeter of the polygon perimeter of the polygon

polygonpolygonpolygon