Continuous Function: Is There an Open Interval Where f is Monotone?

In summary, the question asks if there is an open interval where a continuous function on R is monotone. The answer is yes for non-constant functions, but the "Weierstrasse function" is an example of a continuous function that is not differentiable anywhere. Continuity does not determine if a function is monotone, but knowing whether the derivative is positive or negative around a point can determine monotonicity.
  • #1
sbashrawi
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Homework Statement



Let f be continuous on R. Is there an open interval on which f is monotone?

Homework Equations





The Attempt at a Solution



I think there is such interval for non constant function but I am really not sure.
 
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  • #2
You might want to check out the "Weierstrasse function" which is continuous for all x but differentiable nowhere.
 
  • #3
In general, no.

Continuity doesn't tell you how the fuction approach it's points. If you knew that f '(x) was either negative or postive around some neighbour of your point then you can say if it is monotone or not.
 

FAQ: Continuous Function: Is There an Open Interval Where f is Monotone?

What is a continuous function?

A continuous function is a mathematical function that does not have any sudden jumps or breaks in its graph. This means that the function is defined and can be evaluated at every point along its domain without any gaps or interruptions.

What is an open interval?

An open interval is a set of real numbers between two values, where the endpoints are not included. For example, the open interval (0,1) includes all real numbers between 0 and 1, but does not include 0 or 1 themselves.

What does it mean for a function to be monotone?

A function is said to be monotone if it is either always increasing or always decreasing on a given interval. In other words, the function's values either always increase or always decrease as its input values increase.

Is it possible for a continuous function to not have an open interval where it is monotone?

Yes, it is possible for a continuous function to not have an open interval where it is monotone. For example, a function that oscillates between increasing and decreasing on a small interval would not be monotone on that interval.

How can I determine if a function is monotone on an open interval?

To determine if a function is monotone on an open interval, you can use the first derivative test. If the first derivative of the function is always positive or always negative on the interval, then the function is monotone on that interval. Additionally, you can also graph the function and visually observe if it is always increasing or always decreasing on the interval.

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