Help to prove that an interval will lead to positive functions?

In summary, the conversation revolves around proving the existence of an open interval centered at c such that f(x)>0 for all x that are elements of (a,b), given that f is continuous at c and f(c)>0. The use of the sign preserving property and the epsilon/delta definition of continuity are suggested as approaches to the problem. One user also mentions using the definition of sign preserving property to prove that f(a) and f(b) are positive. Another user is mistaken for posting the same question twice, but clarifies that they did not have multiple accounts.
  • #1
mathkillsalot
25
0

Homework Statement



Let f be continuous at c and f(c)>0. Prove that there is an open interval (a,b) centered at c such that f(x)>0 for all x that are elements of (a,b)

Homework Equations



we are supposed to use the sign preserving property??

The Attempt at a Solution



I tried assigning all x as numbers greater than zero but then realized it wouldn't work since the f(x) is the one that has to be greater than 0. But the function isn't given.
Please help me...
 
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  • #2
Use the epsilon/delta definition of continuity. Pick epsilon=f(c)/2.
 
  • #3
uhmmmm...can you please demonstrate??
and how did you get your epsilon?
 
  • #5
i used the definition of sign preserving property to prove that f(a) and f(b) are positive.
just assigned all x that are elements of (a,b) to be greater than 0...
My answer seemed to be correct...
 
  • #6
but it's not checked yet
 
  • #7
What is this "sign preserving property" you are talking about?
 
  • #9
Do you have multiple accounts ? This is not allowed :-(.

The same question and the same mistake was posted by "another" user in the calculus and beyond section.
 
Last edited:
  • #10
no no i don't. I think I did post this question twice though. Didn't see the forum for homework at first.

though if you're talking about goodheavens, that person might be someone from the same school as me
 
  • #11
mathkillsalot said:
no no i don't. I think I did post this question twice though. Didn't see the forum for homework at first.

though if you're talking about goodheavens, that person might be someone from the same school as me

Okay,sorry about the confusion. :-)
 

Related to Help to prove that an interval will lead to positive functions?

What is an interval in mathematics?

In mathematics, an interval is a range of values between two points on a number line. It can be represented as [a,b] where a and b are the endpoints of the interval.

How do you prove that an interval will lead to positive functions?

To prove that an interval will lead to positive functions, you can use the Intermediate Value Theorem. This theorem states that if a continuous function f(x) takes on two values, f(a) and f(b), at points a and b in an interval [a,b], then it must take on every value between f(a) and f(b) at some point in the interval. If f(a) and f(b) are both positive, then by the Intermediate Value Theorem, all the values in between must also be positive, proving that the interval leads to positive functions.

Can all intervals lead to positive functions?

No, not all intervals will lead to positive functions. For example, an interval that includes negative values or has an endpoint that is equal to or less than zero will not lead to positive functions. Additionally, if the function is not continuous within the interval, the Intermediate Value Theorem cannot be applied and the positivity of the function cannot be proven.

What are some examples of intervals that lead to positive functions?

Examples of intervals that lead to positive functions include [1, 5], (2, 6), and [0, ∞). These intervals all have positive values for both endpoints and the function is continuous within the interval, satisfying the conditions for the Intermediate Value Theorem.

How is proving an interval leads to positive functions useful in science?

Proving that an interval leads to positive functions is useful in science because it allows us to make conclusions about the behavior of a function without having to evaluate every single point. It also helps us identify intervals where the function will have positive values, which can be important in various applications, such as predicting the growth of populations or analyzing data in experiments.

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