Is Function f Continuous at x=0?

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Homework Help Overview

The problem involves determining the continuity of the function f defined on the interval [-1, ∞) with a specific value at x=0. The function is given by f(0) = 1/2 and f(x) = [(1 + x)^(1/2) - 1]/x for x ≠ 0. Participants are tasked with showing that f is continuous at x=0 using the definition of continuity.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss algebraic manipulation of the function to express it in a different form. There are questions about whether an ε-δ proof is necessary or if the limit criterion for continuity can be used instead. Some participants express frustration over the problem and seek suggestions for their approach.

Discussion Status

Several participants have provided insights into the problem, including the identification of the limit as x approaches 0. There is a recognition of the simpler approach involving limits, and some participants express relief at discovering this method. However, no explicit consensus has been reached on the preferred method of proof.

Contextual Notes

There is a note regarding the potential confusion over the function's domain, with one participant suggesting a correction to the domain notation. Additionally, the problem does not specify the requirement for an ε-δ proof, which has led to varied interpretations among participants.

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Homework Statement


Define f:[-1,∞]→ℝ as follows: f(0) = 1/2 and

f(x) =[(1 + x)^(1/2) - 1]/x , if x ≠ 0

Show that f is continuous at 0.


Homework Equations


Definition. f is continuous at xo if xoan element of domain and
lf(x) - f(xo)l < ε whenever lx - xol < δ


The Attempt at a Solution


Do some algebra come up with f(x) = 1/[(1+x)^(1/2) + 1]

I also know that between [-1,1], f(x)≤ 1
and x ≥ 1, f(x) ≤ 1

I know I need to somehow pull out an lxl from the absolute value, since I know lxl≤δ then
I can define δ in terms of ε and the function.
 
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IntroAnalysis said:

Homework Statement


Define f:[-1,∞]→ℝ as follows: f(0) = 1/2 and   That should be f : [-1,∞) → ℝ

f(x) =[(1 + x)^(1/2) - 1]/x , if x ≠ 0

Show that f is continuous at 0.


Homework Equations


Definition. f is continuous at xo if xoan element of domain and
lf(x) - f(xo)l < ε whenever lx - xol < δ


The Attempt at a Solution


Do some algebra come up with f(x) = 1/[(1+x)^(1/2) + 1]

I also know that between [-1,1], f(x)≤ 1
and x ≥ 1, f(x) ≤ 1

I know I need to somehow pull out an lxl from the absolute value, since I know lxl≤δ then
I can define δ in terms of ε and the function.
Do you need to use an ε - δ proof, or can you use the limit criterion for continuity?
If \displaystyle \lim_{x\to x_0}\,f(x)=f(x_0)\,, then f is continuous at x0 .​
 
It just says to show, it doesn't specify δ-ε proof. I've spent hours working on this one problem, any suggestions greatly appreciated!
 
What is the following limit?
\displaystyle <br /> \lim_{x\to0}\,\frac{1}{(1+x)^{1/2} + 1}<br />​
 
It is 1/2 which is f(0).
So this approach I show: 1) the point c is in the domain
2) the limit of f(c) exists and
3) lim x->c f(x)=f(c)

I should have thought of this, it is a lot easier to show. Thank you.
 
IntroAnalysis said:
It is 1/2 which is f(0).
So this approach I show: 1) the point c is in the domain
2) the limit of f(c) exists and   more precisely, lim x→c f(x) exists
3) lim x->c f(x)=f(c)

I should have thought of this, it is a lot easier to show. Thank you.
You're welcome!
 

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