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The parallelogram and its properties

Source: licencja: CC 0.

Równoległobok i jego własności

Learning objectives

You will learn about the properties of the parallelogram.

Learning effect

  • You draw the parallelogram.

  • You calculate the perimeter of the parallelogram.

  • You use English to describe the properties of the parallelogram.

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nagranie abstraktu

Draw the FUKS parallelogramparallelogramparallelogram in your notebook. Then, draw its diagonals.

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Source: epodreczniki.pl, licencja: CC BY 3.0.
Task 1
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nagranie abstraktu

Open the applet and watch how the lengths of the diagonals, the values of the angles of the intersection of the diagonals change due to change of the length of the sides of the parallelogramparallelogramparallelogram.

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Aplet geogebry: Równoległobok. Poniżej znajduje się galeria ilustracji stanowiących alternatywę dla apletu.
Source: GroMar, licencja: CC BY 3.0.
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nagranie abstraktu

After completing the task, answer the following question:

  • What can you say about the length of the diagonals of the parallelogramparallelogramparallelogram?

  • Is it possible for the parallelogramparallelogramparallelogram to have all sides equalequalequal in length and differentdifferentdifferent diagonals?

  • Can the angleangleangle of the intersection point be the right one and the diagonals be of the same length? Can they be differentdifferentdifferent?

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nagranie abstraktu

You should notice that:

  • the diagonals of the parallelogramparallelogramparallelogram, which is not a rectangle, are of differentdifferentdifferent length,

  • if the diagonals of the parallelogram are equalequalequal in length, the parallelogramparallelogramparallelogram is a rectangle,

  • the diagonals of the parallelogramparallelogramparallelogram are divided into halves,

  • the diagonals of the parallelogram are not perpendicular, if its adjacent sides are differentdifferentdifferent in length,

  • the diagonals of the parallelogramparallelogramparallelogram are perpendicular, if its adjacent sides are equalequalequal in length. Such parallelogramparallelogramparallelogram is called a rhombus.

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Source: epodreczniki.pl, licencja: CC BY 3.0.
Task 2
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nagranie abstraktu

Measuremeasure Measure all interior sides of the parallelogramparallelogramparallelogram.

After completing the task, answer the following questions:

  • What can you say about the opposite anglesopposite anglesopposite angles of the parallelogram?

  • What is the sum of all interior angles of the parallelogramparallelogramparallelogram?

  • What is the sum of the angles situated on the same sidesideside?

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nagranie abstraktu

Conclusions:

  • Opposite anglesopposite anglesOpposite angles are equalequalequal.

  • The sum of all angles of the parallelogramparallelogramparallelogram equals 360°.

  • The sum of the angles situated on the same sidesideside equals 180°.

Task 3
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nagranie abstraktu

Students calculate the missing values of the angles of the parallelogramparallelogramparallelogram on their own. They know that one of the angles is 50°.

Task 4
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nagranie abstraktu

Students draw a parallelogramparallelogramparallelogram with sides of 5 cm and 3 cm on their own and calculate its perimeter.

Task 5
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nagranie abstraktu

Students draw a rhombus on their own. The perimeter of the rhombus is 36 cm and the acute angleangleangle is 30°.

Task 6

An extra task:

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nagranie abstraktu

Find out on the Internet how to construct the parallelogramparallelogramparallelogram knowing the length of its sides.

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nagranie abstraktu

Remember:

  • The parallelogramparallelogramparallelogram is a quadranglequadranglequadrangle with two pairs of parallel sides. The parallel sides of the parallelogramparallelogramparallelogram are equalequalequal in length.

  • The perimeter of a parallelogramparallelogramparallelogram is the sum of all its sides.

  • Opposite anglesopposite anglesOpposite angles are equalequalequal. The sum of angles lying at the same sidesideside is 180°. The sum of all angles in a parallelogramparallelogramparallelogram is 360°.

  • The diagonals of a parallelogramparallelogramparallelogram (which is not a rectangle) are of differentdifferentdifferent length and they divide into halves.

Check what you have learned by completing the following exercises.

Exercises

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Exercise 1
Wersja alternatywna ćwiczenia: Determine which sentences are true. Możliwe odpowiedzi: 1. Each rectangle is a parallelogram., 2. Each parallelogram with a right angle is a rectangle., 3. Each parallelogram with perpendicular diagonals is a square., 4. Each parallelogram is a rectangle., 5. Each parallelogram with all equal sides is a square.
zadanie
Exercise 2

In the drawing you can see two sides of a parallelogram which are of different lengths. Complete the figure of the parallelogram.

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Source: GroMar, licencja: CC BY 3.0.
Exercise 3

Draw the following parallelogram. One of its sides is 6 cm, the other one is 2 cm longer and the acute angle of the parallelogram is 45°. Calculate the perimeter of the parallelogram.

Describe the construction of the parallelogram in English.

Exercise 4
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Wersja alternatywna ćwiczenia: Indicate which pairs of expressions or words are translated correctly. Możliwe odpowiedzi: 1. przekątna - diagonal, 2. różne - different, 3. równe - equal, 4. równoległobok - parallelogram, 5. kwadrat - quadrangle, 6. odcinek - side
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

angle
angle

kąt

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wymowa w języku angielskim: angle
diagonal
diagonal

przekątna – odcinek łączący dwa wierzchołki wielokąta, który nie jest bokiem

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wymowa w języku angielskim: diagonal
different
different

różne

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wymowa w języku angielskim: different
equal
equal

równe

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wymowa w języku angielskim: equal
measure
measure

miara

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wymowa w języku angielskim: measure
opposite angles
opposite angles

kąty leżące naprzeciwko

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wymowa w języku angielskim: opposite angles
parallelogram
parallelogram

równoległobok – czworokąt, który ma dwie pary boków równoległych

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wymowa w języku angielskim: parallelogram
quadrangle
quadrangle

czworokąt

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wymowa w języku angielskim: quadrangle
side
side

bok

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wymowa w języku angielskim: side

Keywords

angleangle angle

diagonaldiagonal diagonal

parallelogramparallelogramparallelogram

quadranglequadranglequadrangle

sideside side