Counter examples to disprove mappings?

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Is it still monotonic?In summary, a real valued odd function can be strictly monotonic, as demonstrated by the function sinh(x). Counterexamples can also be given for the statements that a real valued periodic function must be odd or even, and that a real valued monotonic function cannot be even. By phase shifting a periodic function, it can be transformed into one that is neither even nor odd. Additionally, by shifting an odd periodic function up or down, it can still maintain its monotonicity.
  • #1
xlalcciax
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give counter examples to disprove the following statements:
a) a real valued odd function cannot be strictly monotonic
b) a real valued periodic function must be odd or even
c) a real valued monotonic function cannot be even


a) sinh(x) ??
b)
c)
 
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  • #2
Yes, (a) is correct!
 
  • #3
micromass said:
Yes, (a) is correct!

Thanks!
Can You give me some clues for b) ?
 
  • #4
Pick your favorite periodic function and transform it so that it is neither even nor odd...
 
  • #5
xlalcciax said:
Thanks!
Can You give me some clues for b) ?

Think of a periodic function that is odd or even. Now phase shift it slightly. Is it still odd or even?
 
  • #6
nicksauce said:
Think of a periodic function that is odd or even. Now phase shift it slightly. Is it still odd or even?


yeah. i have got it now!
what about c) ? f(x)=2 ??
 
  • #7
xlalcciax said:
Thanks!
Can You give me some clues for b) ?
Any odd function which is continuous on (−∞, +∞), passes through the origin.

Take an odd periodic function & shift it up or down.
 

Related to Counter examples to disprove mappings?

1. What is a counter example in the context of mappings?

A counter example is a specific example or instance that disproves a general statement or mapping. In other words, it is a situation or scenario that goes against the proposed mapping, thus showing that the mapping is not always true.

2. How are counter examples used to disprove mappings?

Counter examples are used to show that a proposed mapping is not always true by providing a specific instance where the mapping does not hold. This proves that the mapping is not universally valid and therefore cannot be considered as a valid rule or statement.

3. Can a counter example completely disprove a mapping?

Yes, a single counter example can be enough to disprove a mapping. This is because the mapping is meant to hold true for all possible scenarios, and a single instance where it does not hold is enough to show that it is not a universally true statement.

4. Are counter examples only used in mathematical mappings?

No, counter examples can be used in various fields and contexts, not just in mathematics. They can be used to disprove hypotheses, theories, and general statements in any field of study, as long as there is a clear mapping or relationship being proposed.

5. Can counter examples be used to prove a mapping?

No, counter examples are only used to disprove mappings. If a counter example is found, then the mapping is considered invalid. However, multiple examples that support a mapping can be used to provide evidence for its validity, but they cannot prove it definitively.

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