# How to notate a variable that is being held constant

I remember learning at one point that you can put some sort of symbol on top or near a variable to indicate that it is being held constant. I thought that it was just a bar drawn above the variable but in some cases, it means "the average of."

Anyone know what I'm talking about?

## Answers and Replies

I remember learning at one point that you can put some sort of symbol on top or near a variable to indicate that it is being held constant. I thought that it was just a bar drawn above the variable but in some cases, it means "the average of."

Anyone know what I'm talking about?
Do you mean that, when taking a partial derivative and want to specifically keep t constant, you can write, for example, ##\left(\frac{\partial f}{\partial x}\right)_t##?

Do you mean that, when taking a partial derivative and want to specifically keep t constant, you can write, for example, ##\left(\frac{\partial f}{\partial x}\right)_t##?
No, I mean something much simpler. It's a symbol or notation that you'd use as you're explaining how variables will change relative to each other.

Here's a very simple example using the equation d=vt (distance = speed*time):

Say I want to hold the speed at a constant value; I now know that by increasing the amount of time, I'll increase the value of the distance by a proportionate amount. My question involves a short-hand symbol for indicating that the speed is the variable that's being held constant, instead of wasting time writing out "___ is constant" everytime I'm discussing an equation.

In spreadsheet programs like excel this is done by putting '$' '$' around the variable, though I doubt that's what you're looking for.

Do you mean just saying:
##D= \frac{v}{t} \rightarrow D= \frac{v_1}{t}##? Because that sort of does it.

Do you mean just saying:
##D= \frac{v}{t} \rightarrow D= \frac{v_1}{t}##? Because that sort of does it.

That's more like it, but not exactly what I had in mind.

It's such a dumb little thing but it's driving me nuts.

Thanks for the reply

That's more like it, but not exactly what I had in mind.

It's such a dumb little thing but it's driving me nuts.

Thanks for the reply
What class was it? That might help?

What class was it? That might help?
It's not for a specific class. I tutor for math and physics and there are times when I want to denote which variable in the equation is being held constant for the sake of discussing how the other variables effect each other.

I remember a math (or science) teacher I had in high school making a mark near the variable that would be held constant.

Mute
Homework Helper
It's not for a specific class. I tutor for math and physics and there are times when I want to denote which variable in the equation is being held constant for the sake of discussing how the other variables effect each other.

I remember a math (or science) teacher I had in high school making a mark near the variable that would be held constant.
I'm not familiar with any standard notation that denotes what you want. You could make one up for the students you are tutoring, but let them know it's not a notation they're likely to see elsewhere.

You could say something like "let d = x(t) = vt", where the function notation x(t) explicitly denotes that t is the variable. If the students need a mark to remind them which symbols are constants, function notation may at first be confusing for them, but it's a notation they will likely see again in the future.

jbriggs444