You will learn to apply direct proportionality in exercises.
Learning effect
You apply direct proportionality in exercises.
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Revise the definition of direct proportionalitydirect proportionalitydirect proportionality.
Direct proportionality
Definition: Direct proportionality
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Direct proportionality is a relation between two variables x and y, defined by the formula y = a · x. The number a, different from zero, is called the coefficient of proportionality.
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Where in everyday situations we can find directly proportional values? Give examples.
If you answer 3 questions correctly, you are the champion.
1. A worker makes 16 details in an hour. How many details will he make in 1,5 hours?
2. In 8 hours a pump pumps 72 litres of water. How many litres will it pump in 2 hours?
3. A car uses on average 4 litres of gasoline on 55 km distance. How many kilometres can the car make if it uses on average 14,5 litres of gasoline?
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Task 1
Your task is to observe the relation between the length of the diagonal of a square and the length of its side.
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Identify with a formula the relation between the altitude of the equilateral triangle and the length of its side.
Use obtained information in the exercises.
Task 2
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Five packages of cheese cost 17 zł. Will 27 zł be enough to buy eight packages of this cheese?
Task 3
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1 l box of milk costs 2,80 zł. How does the cost of all shopping change depending on the bought amount of boxes of milk? Draw a table describing the amount of bought boxes of milk, in the range {2, 3, 4, 5, 6, 7}, in relation to their price.
Task 4
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Let’s consider all rectangles whose one side is equal to 5. Is the area of this triangle directly proportional to the length of the other side? If yes, give the formula coefficient of proportionality and draw a plot of this relation.
Task 5
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A train travelled 150 km in 2,5 hours. How many kilometres did it travel in 1,25 hours if it was going with the same speed?
Task 6
An extra task:
Is a side of an equilateral triangle and a radius of a circle inscribed in this triangle directly proportional? If yes, give the formula and the coefficient of proportionality.
Do the revision exercises.
Exercises
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Exercise 1
Exercise 2
Write a formula determining the relation between the perimeter of an equilateral triangle and its side. Draw a plot of this relation assuming that the length of the triangle belongs to the range (1, 5).
y = 3x.
Exercise 3
Are distance and time in uniform motion values directly proportional?
Describe the answer in English.
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Exercise 4
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Glossary
direct proportionality
direct proportionality
proporcjonalność prosta
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formula of the function
formula of the function
wzór funkcji
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line
line
prosta
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plot of the function
plot of the function
wykres funkcji
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values directly proportional
values directly proportional
wielkości wprost proporcjonalne
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Keywords
direct proportionalitydirect proportionalitydirect proportionality – funkcja opisująca zależność między wielkościami wprost proporcjonalnymi