Derivative of Constant: Proving f(x) is Constant

In summary, the conversation discusses different methods for proving that a function is constant if its derivative is equal to zero. These methods include using the definition of the derivative and the mean value theorem.
  • #1
Suvadip
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If \(\displaystyle f(x)\) is constant then I can show that \(\displaystyle f'(x)=0\).
But if \(\displaystyle f'(x)=0\), then how to show that \(\displaystyle f(x)\) is constant ?
 
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  • #2
Re: derivative of constant

What does the definition of the derivative tell you?

edit: Sorry, I misread...have you tried integrating with respect to the independent variable?
 
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  • #3
Re: derivative of constant

suvadip said:
If \(\displaystyle f(x)\) is constant then I can show that \(\displaystyle f'(x)=0\).
But if \(\displaystyle f'(x)=0\), then how to show that \(\displaystyle f(x)\) is constant ?

Another approach would be to use differentials:
$$\Delta y=f'(x)\, \Delta x = 0 \cdot \Delta x \, ...$$
 
  • #4
Re: derivative of constant

suvadip said:
If \(\displaystyle f(x)\) is constant then I can show that \(\displaystyle f'(x)=0\).
But if \(\displaystyle f'(x)=0\), then how to show that \(\displaystyle f(x)\) is constant ?
The mean value theorem: if f is continuous and differentiable on [a, b] then there exist c in [a, b] such that [tex]f'(c)= \frac{f(b)- f(a)}{b- a}[/tex]. If f'(x)= 0 for all x, then for any a and b, [itex]\frac{f(b)- f(a)}{b- a}= 0[/tex] from which f(a)= f(b).
 

FAQ: Derivative of Constant: Proving f(x) is Constant

What is a derivative?

A derivative is a mathematical concept that represents the rate of change of a function at a specific point. It is essentially the slope of the tangent line to the function at that point.

How do you prove that a function is constant using derivatives?

To prove that a function f(x) is constant, you need to show that its derivative, f'(x), is equal to 0 for all x values. This means that the function's rate of change is 0, indicating that it is not changing and therefore constant.

Why is it important to know how to prove a function is constant?

Knowing how to prove that a function is constant using derivatives is important in understanding the behavior and characteristics of functions. It also allows for the identification of constant functions, which are often used as a starting point for more complex mathematical concepts.

What is the formula for the derivative of a constant function?

The derivative of a constant function f(x) = c, where c is any constant, is equal to 0. In other words, the derivative of a constant function is always 0.

Can you give an example of proving a function is constant using derivatives?

For example, let's take the function f(x) = 5. To prove that this function is constant, we can take its derivative, which is f'(x) = 0. This shows that the function has a constant rate of change of 0, and therefore it is a constant function.

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