What is the unit of this "Rate of Change"? This is the plot of the function f(x)=0.9x. So, the rate of change of y with respect to x is 0.9. My question is, what is the unit of this Rate of Change? 0.9 per x?

Dawson Downs

Dawson Downs

Answered question

2022-07-20

What is the unit of this "Rate of Change"?
the function f ( x ) = 0.9 x
So, the rate of change of y with respect to x is 0.9.
My question is, what is the unit of this Rate of Change?
0.9 per x?

Answer & Explanation

cindysnifflesuz

cindysnifflesuz

Beginner2022-07-21Added 19 answers

Well, it really depends on context. In a very pure sense, the slope does not have units in this context. In a more vernacular sense, it's common to have things like
y = # of meters travelled of meters travelled
x = # of seconds passed of seconds passed
Then write y=2x as a relationship. Then, the units of slope would be meters/second, meaning that two meters pass (on the y-axis) for every one second on the x-axis. So, the units here are the units of the y-axis divided by those of the x-axis.
However, it's worth noting that this relationship might be better written as f ( x  seconds ) = 2 x  meters
where you recognize that the function f takes in a duration and spits out a length - and that the units are not an intrinsic quality of the function. In this sense, you could justifiably write for the same function that
f ( x  minutes ) = 120 x  meters .
An equivalent way to write this function is as follows:
f ( t ) = ( 2  meters/second ) t
where you note that if you plug in x seconds for t, you get 2x meters. This last point of view shows that the slope is just the coefficient multiplied by the input - and it is very often desirable to treat these slopes as intrinsically having units which are part of the value, not an interpretation thereof.
In an abstract setting (or a setting where the input and output are both distances or both times or generally both the same), the slope does not have units. It is just 0.9.
Graham Beasley

Graham Beasley

Beginner2022-07-22Added 3 answers

If you would put units for x and y, say time in seconds for x and distance in meters for y, the slope is in meters/second. So in the general case, the unit for the rate of change is "units of y divided by units of x". You can use "per" instead of "divided by".

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