How to define this function

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In summary, the given conditions do not guarantee that g(x) is continuous. A counter example is provided where f(x) < g(x) < h(x) and f and h are continuous, but g is not continuous at x = 0. Another simpler counter example is also mentioned where g is discontinuous for all x.
  • #1
Cacophony
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Homework Statement



If f(x) < g(x) < h(x) for all x E R, and if f and h are continuous functions, must g also be continuous? If so, why? If not, can you come up with a counter example?

What do you think?
 
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  • #2
Hi...
For the given conditions ,the function g need not be continuous.
Example : f(x) = sin(x) - 3 , h(x) = sin(x) + 3 , g(x) = sin(1/x)
for this example , f(x) < g(x) < h(x) . f and h are continuous . But g is not continuous at x tends to 0. Instead of g(x) = sin(1/x) , u can also take a signum function which is not continuous at x = 0.
 
  • #3
Blazeatron's example is sufficient but simpler-
f(x)= 0 for all x, h(x)= 3 for all x, g(x)= 1 if x is rational, 2 if x is irrational. g is discontinuous for all x.
 

1. What is a function?

A function is a mathematical relationship between inputs (also called "arguments" or "parameters") and the resulting output. It can also be thought of as a machine that takes in certain inputs and produces a specific output.

2. How do you define a function?

To define a function, you need to specify the input(s), the mathematical operations or formula to be performed on the input(s), and the resulting output. This is typically done using functional notation, where the function is named and the input(s) are surrounded by parentheses.

3. What is the difference between a function and a variable?

A function is a mathematical relationship between inputs and outputs, while a variable is a placeholder for a value. In other words, a function takes in inputs and returns outputs, while a variable simply holds a value.

4. Can a function have more than one input?

Yes, a function can have multiple inputs. This is known as a multivariate function. The number of inputs a function has is known as its "arity". Some functions may have a fixed number of inputs, while others may have a varying number of inputs depending on the context.

5. How do you determine the domain and range of a function?

The domain of a function is the set of all possible inputs, while the range is the set of all possible outputs. To determine the domain and range of a function, you can use mathematical techniques such as finding the intercepts, determining the intervals where the function is defined, or using algebraic methods such as finding the inverse function. It is important to note that the domain and range of a function may be limited by the context in which the function is being used.

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