Prove an odd function is strictly increasing

In summary, the conversation discusses proving that if a function f:R->R is odd and its restriction to the interval [0, infinity) is strictly increasing, then the entire function f:R->R is also strictly increasing. The proof involves examining the behavior of the function on the interval (-\infty, 0) and using the fact that f is continuous and strictly increasing in [0, infinity).
  • #1
xsw001
37
0
f:R->R is odd, if f(-x)=-f(x) for all x
Show if f:R->R is odd and the restriction of this function to the interval [0, infinity) is strictly increasing
Then f:R->R itself is strictly increasing

I’m very confused about what the question is exactly asking for. From my understanding of the question is that I have any odd function and the graph is strictly increasing in the first quadratic . I need to prove entire graph of such odd function is strictly increasing? Am I interpreting it correctly?
I know how to prove for a strictly increasing function. Let u, v in R, find f(v)-f(u)>0, then f:R->R is strictly increasing function.

Proof:
Given f is an odd function and f is strictly increasing in [0, infinity)
Then f(D) = I, the image of the function is an interval
Therefore f is continuous and strictly increasing?
 
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  • #2
Just examine the behavior of the function on the interval [tex](-\infty, 0)[/tex].
 
  • #3
Okay, got it!
 
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1. What is an odd function?

An odd function is a mathematical function that satisfies the property f(-x) = -f(x) for all values of x. This means that if you plug in a negative value for x, the output will be the negative of the output when plugging in the positive value of x. In other words, the graph of an odd function is symmetrical with respect to the origin.

2. What does it mean for a function to be strictly increasing?

A strictly increasing function is one in which the output values (y) increase as the input values (x) increase. In other words, as you move from left to right on the graph, the y-values are always getting larger. The graph of a strictly increasing function will never decrease or stay the same.

3. How can you prove that an odd function is strictly increasing?

To prove that an odd function is strictly increasing, you can show that the derivative of the function is always positive. This means that the slope of the graph is always positive and is never 0 or negative. Another way to prove this is by showing that the function satisfies the property f'(x) > 0 for all values of x.

4. Can an odd function be strictly increasing and strictly decreasing at the same time?

No, an odd function cannot be strictly increasing and strictly decreasing at the same time. This is because if a function is strictly increasing, it means that the graph is always moving upwards, while if a function is strictly decreasing, the graph is always moving downwards. An odd function, by definition, cannot have both of these properties at the same time.

5. Are there any special cases where an odd function is not strictly increasing?

Yes, there is one special case where an odd function is not strictly increasing. This is when the function is identically equal to 0, meaning that the output is always 0 regardless of the input. In this case, the function is neither increasing nor decreasing. However, this is the only exception and all other odd functions will be strictly increasing.

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