Prove: Increasing Function f(x) Has a Positive Value at a

In summary, to prove that there is a number "a" where f(a) > 0 for an increasing and concave up function f(x), one can start by picking an arbitrary x0 in the domain and making estimates for f(x) in terms of f(x0) and positive quantities until an x = a is found where f(a) > 0.
  • #1
Ki-nana18
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Homework Statement



Suppose that a function f(x) is increasing and concave up. Show that there is a number "a", such that f(a)>0.

The Attempt at a Solution



How would I go about showing this?
 
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  • #2
What do "increasing" and "concave up" mean (in terms of derivatives)?

I think the best way to start the proof is: Pick an arbitrary x0 in the domain.
Then either f(x0) > 0 and you are done, or f(x0) <= 0. Now probably your intuition tells you that somewhere to the right of x0, f must become positive, right?
You can formalise that by taking some x > x0, and making estimates for f(x) in terms of f(x0) and positive quantities, until you find an x = a such that f(a) > 0.
 

FAQ: Prove: Increasing Function f(x) Has a Positive Value at a

What is an increasing function?

An increasing function is a mathematical function where the value of the function increases as the input variable increases. In other words, as the value of x increases, the value of f(x) also increases.

How can you prove that a function is increasing?

To prove that a function is increasing, you can use the definition of an increasing function which states that for any two inputs x1 and x2, if x1 < x2, then f(x1) < f(x2). This means that for any two points on the function, the y-value of the first point will be less than the y-value of the second point.

What is the importance of proving that a function is increasing?

Proving that a function is increasing is important because it allows us to make accurate predictions about the behavior of the function. It also helps us to understand the relationship between the input and output variables and can be used to solve real-world problems.

What does it mean for a function to have a positive value at a specific point?

When a function has a positive value at a specific point, it means that the output or y-value of the function at that point is greater than zero. This indicates that the function is increasing at that particular point.

Can a function be increasing and have a negative value at a specific point?

No, if a function is increasing, it cannot have a negative value at a specific point. This is because an increasing function by definition means that the value of the function increases as the input variable increases. Therefore, it cannot have a negative value at any point along the function.

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