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### Course: 7th grade (Illustrative Mathematics)>Unit 2

Lesson 6: Lesson 7: Comparing relationships with tables

# Is side length & perimeter proportional?

Sal answers the question by drawing a square and thinking about the relationship between side length and perimeter.

## Want to join the conversation?

• what does proportional mean??
• or this (of two quantities) having the same or a constant ratio or relation:
The quantities y and x are proportional if y/x = k, where k is the constant of proportionality.
• Are the length and breadth of different rectangles of the same perimeter in proportion. Examine.
• I understand this for a sqaure, but what If it's for a rectangle how would te sides be porportional since a rectangles has not all 4 sides that are congurent.
• If this is for a rectangle, the ratio won't be proportional any more. For rectangles can have any number from 1 to infinity for two of the sides and another number from 1 to infinity for the other two sides. If the 4 sides are the same, you get a special rectangle that you call a square.
For example, two sides of the rectangle are 4 and the other two are 6. Then the perimeter would be 4+4+6+6 which is 20, then do 20 divided one of the sides to get the proportion, for example, 20 divided 4, then you will get 5. Then get another rectangle, let's say two sides are 7 and the other two are 9. then you would have 32 for the perimeter, then 32 divided 8, and you get 4.
And now we have a proportion of 5 and another of 4. This is not a proportional relationship.
Hopefully this helps.
• What happens when you only have x on one side?
• well it can depend on what the other sides are since you said that one side of the square is x then all of the other sides are x as well ( all sides of a square are equal)
(1 vote)
• Is this directly proportional or inversely proportional? Especially if we're looking for the perimeter of a rectangle.
• Nice cool doing this with us
• why do you repeat when you say "side length" because then i hear "siiiiiide length, side length"
• side length
(1 vote)
• How can ratio's help us in REAL LIFE.