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# Identifying constant of proportionality graphically

Sal identifies the constant of proportionality from a line graphed on a coordinate plane.

## Want to join the conversation?

• I'm confused at the constant of proportionality
• The constant of proportionality is what determines the relationship between y and x. If r is the constant of proportionality then an example is y = rx . The value of y is dependant on how the given value of x is effected by the constant of proportionality.
• why dont i get thisbut everyone else does
• Why did you use a k and not a c to represent constant?
• Nobody knows for sure why. But it is strongly believed that k is used as constant almost everywhere, because the German word for ‘constant’ is ‘konstante’. The first letter of that word is k. And the Germans contributed in mathematics hugely since the dawn of it.
While c is used for many other tasks and usually is not available.
• I know we normally use y=kx equation but is there a reason to use ky=x instead? Also how would you know when to use each equation?
• we do not use ky=x instead because it is incorrect. But if you mean y/k=x or y/x=k, which is correct, and we sometimes use it because we feel like it and it is another way of solving constant of proportionality.
• Can someone help me?

We can calculate E, the amount of euros that has the same value as D U.S. dollars, using the equation E = 17/20 D

How many euros have the same value as 1 U.S. dollar?

How many U.S. dollars have the same value as 1 euro?
• According to the formula, 1 dollar is equal to (17∕20) ∙ 1 = 0.85 euros.

Also, multiplying a fraction by its reciprocal gives 1, so in order to get 1 euro we would need 20∕17 ≈ 1.18 dollars
• When Sal said y=x, does that mean that any point on the line for y or x, will equal each other?
• Yes. For any point on the line y = x, the x and y of the point will equal each other.
• Well, I don't understand how to identify constant of proportionality graphically.
(1 vote)
• The constant of proportionality is the slope of a line that goes through the origin (0,0).
• did anyone hear sal say fot at cause i have english auto generated captions on?