How can we prove the continuity of ln x over (0, ∞)?

In summary, to prove that lnx is continuous over (0, ∞), we can use the definition of lun x = y <=> e^y = x and the property lnx - lnu = ln(x/u). By fixing x > 0 and letting u approach x, we can show that x/u approaches 1 and ln1 = 0. This proof may need the assumption of ey being continuous and the continuity of lnx for x = 1.
  • #1
evagelos
315
0
how can we prove that lun x is continuous over (0, [tex]\infty[/tex] )?

Provided that we define : lun x =y <=> [tex]e^y =x[/tex]?
 
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  • #2


lnx - lnu = ln(x/u). For any fixed x > 0, u->x => x/u -> 1 and ln1=0.

You can dress this proof up.
 
  • #3


mathman said:
lnx - lnu = ln(x/u). For any fixed x > 0, u->x => x/u -> 1 and ln1=0.

You can dress this proof up.

Can you elaborate a little more ? I do not how to start
 
  • #4


I am not sure what you are given to start with. For example are you assuming ey is continuous? My proof (I admit) is somewhat flawed. It needs continuity of ln(x) for x=1, which then implies continuity for all x.
 

1. What is the definition of continuity?

Continuity is a concept in mathematics that describes the behavior of a function at a specific point. A function is considered continuous if it is defined at that point and there are no sudden jumps or breaks in its graph.

2. How do you prove continuity of a function?

To prove continuity of a function, you must show that the function is defined at a specific point, the limit of the function exists at that point, and the limit is equal to the value of the function at that point.

3. What is the difference between continuity and differentiability?

Continuity and differentiability are related concepts, but they are not the same. Continuity refers to the behavior of a function at a specific point, while differentiability refers to the existence of the derivative of a function at a point.

4. Can a function be continuous at a point but not differentiable?

Yes, a function can be continuous at a point but not differentiable. This can occur if the function has a sharp corner or cusp at that point, which would make the derivative undefined.

5. How do you find the continuity of a function on a closed interval?

To find the continuity of a function on a closed interval, you must check the continuity of the function at each endpoint of the interval and at every point in between. If the function is continuous at all of these points, then it is considered continuous on the closed interval.

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