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# Constant of proportionality from equation

Sal identifies the constant of proportionality from equations.

## Want to join the conversation?

• does anyone else not get this 😌🙃
• I don't get it.😔
(1 vote)
• Is there a specific reason that you always solve for y, and not x?
• You normally solve the constant of proportionality for first number to second number.
• how are you able to tell 4 is not 1/2 if it only says 4/x , the x could =8?
• y = 4/x
What this equation tells you is that for whatever value of x, y will equal 4 divided by that value.
Here, x and y are variables, their value changes.
This means that the y-value depends on the x-value. They need not be fixed : x and y can equal anything, but their product will always be four.
The constant of proportionality here is the 4, because it is the only thing which has a fixed value.

P.S. : This is a different type of proportion, called inverse proportion. Here, as one variable increases, the other decreases and vice-versa. The equation is in the form of y = k*1/x.
Hope this helps :)
• Honestly this is kinda lame like were never gonna do this in the real world Right?
• My mom randomly makes me Do it
• why do we do these
• FOR REAL why do we do these are we gonna do this in real life like
• at how did you get 1/2 dont u do 6 divided by 3 is 2? im a little confused?
• 3/6 is the same as 1/2 because 3 times 2 is 6
• What happens if the problem your trying to solve has a decimal? For Example: y = 2.5x ?
• That's ok. The constant of proportionality can be a decimal, fraction, integer, or any real number.
• Question one doesn't make sense to me,

So we have

4y = 8x

so for Y=KX We find what times X = Y or Y/X. 4/8 (Y/X) not 8/4 (X/Y)

So Y=1/2 . 8X = 4,

but Sal wrote Y=2X 2 . 8X = 16 not our Y = 4
• If you are starting with: 4y=8x, you need to divide both sides by 4 to find the constant of proportionality. You get:
y = 2x
The constant of proportionality = 2
The value of Y will always be 2 times the value of X.

Hope this helps.