Checking if f(x)=x^3 is Monotonic: No Derivatives Needed

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  • Thread starter Yankel
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In summary, to check if a function is monotonic without using derivatives, you can look for patterns in the function's values or plot it on a graph. A monotonic function is one that always increases or decreases, without changing direction on any interval of its domain. It cannot be both increasing and decreasing at different intervals. The graph of a monotonic function will have a constantly increasing or decreasing trend, without any local maximum or minimum points. It is possible for a function to be monotonic but not continuous, as continuity takes into account the function's behavior at specific points.
  • #1
Yankel
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Hello,

I want to check if

f(x)=x^3 is monotonically increasing or monotonically decreasing or not monotonic at all.

How do I do that, without using derivatives yet ?

Thanks !
 
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  • #2
You use the definition.
 
  • #3
Let $h$ be some positive real number, then if:

\(\displaystyle f(x+h)-f(x)\ge0\) the function is monotically increasing or if:

\(\displaystyle f(x+h)-f(x)\le0\) the function is monotically decreasing.
 

Related to Checking if f(x)=x^3 is Monotonic: No Derivatives Needed

1. How do I check if a function is monotonic without using derivatives?

To check if a function is monotonic without using derivatives, you can look for patterns in the function's values. If the function's values consistently increase or decrease as the input increases, then it is monotonic. Another method is to plot the function on a graph and see if it has an overall increasing or decreasing trend.

2. What is the definition of a monotonic function?

A monotonic function is a function that either always increases or always decreases as the input increases. In other words, the function's values do not change direction (from increasing to decreasing or vice versa) on any interval of its domain.

3. Can a function be both increasing and decreasing at different intervals?

No, a function cannot be both increasing and decreasing at different intervals and still be considered monotonic. Monotonicity applies to the entire domain of the function, so if it changes direction at any point, it is not considered monotonic.

4. How does the graph of a monotonic function look like?

The graph of a monotonic function can either have a constantly increasing trend (for a strictly increasing function) or a constantly decreasing trend (for a strictly decreasing function). It will not have any local maximum or minimum points, and the graph will never cross its own curve.

5. Is it possible for a function to be monotonic but not continuous?

Yes, it is possible for a function to be monotonic but not continuous. Monotonicity only depends on the function's values, while continuity also takes into account the function's behavior at specific points. So, a function can have a consistent increasing or decreasing trend but still have points of discontinuity.

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