Partial derivative equals zero means it is constant?

In summary, if \frac{\partial u}{\partial x} = 0, then u is independent of x and is u=f(y,z) only. This means that the value of u does not change whenever x changes, and u is not a function of x, but rather a function of y and z only.
  • #1
crocomut
17
0
Suppose we have a function

[tex]u=f(x,y,z)[/tex]

If [tex]\frac{\partial u}{\partial x} = 0[/tex]

then u is independent of x and is
[tex]u=f(y,z)[/tex]
only.

Correct?
 
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  • #2
crocomut said:
Suppose we have a function

[tex]u=f(x,y,z)[/tex]

If [tex]\frac{\partial u}{\partial x} = 0[/tex]

then u is independent of x and is
[tex]u=f(y,z)[/tex]
only.

Correct?

Correct. Think about it. If [itex]\frac{\partial u}{\partial x} = 0[/itex], this means that the value of u does not change whenever x changes. i.e. u does not depend on x.
 
  • #3
gb7nash said:
Correct. Think about it. If [itex]\frac{\partial u}{\partial x} = 0[/itex], this means that the value of u does not change whenever x changes. i.e. u does not depend on x.


It's interesting to contemplate the distinction between saying "u does not depend on x" and "u is not a function of x". For example, in the case of a single variable, the function that maps all real numbers to 3, which we write as f(x) = 3, is a constant function. But some people say it is "not a function of x" when they mean it "does not depend on x".
 

Related to Partial derivative equals zero means it is constant?

1. What does it mean when a partial derivative equals zero?

When a partial derivative equals zero, it means that the rate of change of a multivariable function in a specific direction is equal to zero. This indicates that the function is not changing in that direction.

2. Does a partial derivative of zero always mean the function is constant?

No, a partial derivative of zero does not always mean the function is constant. It only means that the function is not changing in a specific direction. The function may still be changing in other directions, resulting in a non-constant function.

3. Can a function have a constant partial derivative but still not be constant?

Yes, a function can have a constant partial derivative but still not be constant. This is because the function may be changing at a constant rate in one direction, but changing at a different rate in another direction. Therefore, the overall function is not constant.

4. How can partial derivatives help determine constant functions?

Partial derivatives can help determine constant functions by showing where the function is not changing. If all partial derivatives of a multivariable function are equal to zero, then the function is constant in all directions.

5. Are there any other conditions besides a partial derivative of zero that indicate a function is constant?

Yes, there are other conditions besides a partial derivative of zero that indicate a function is constant. These include having a constant value for all inputs, having a slope of zero at all points on the function, and having a constant rate of change in all directions.

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