Limit of ((x2+y2+1)1/2) - 1: Evaluate & Simplify

  • Context: MHB 
  • Thread starter Thread starter Jamie2
  • Start date Start date
  • Tags Tags
    Limit
Click For Summary

Discussion Overview

The discussion centers on evaluating and simplifying the limit of the expression \(((x^2+y^2+1)^{1/2}) - 1\) as \((x, y)\) approaches \((0, 0)\). Participants explore different methods for finding the limit, including algebraic simplification and polar coordinates.

Discussion Character

  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant claims the limit equals 0 by simplifying the expression and evaluating it directly at \((0, 0)\), but questions the correctness of this approach.
  • Another participant suggests that converting to polar coordinates yields a different result, referencing confirmation from Wolfram Alpha.
  • A request for clarification on the polar coordinate method is made, indicating some confusion about the approach.
  • A later reply outlines the polar coordinate transformation, stating that the limit can be expressed as \(\lim_{r\to0}\left(\frac{r^2}{\sqrt{r^2+1}-1} \right)\) and mentions the possibility of using L'Hôpital's Rule after rationalizing the denominator.

Areas of Agreement / Disagreement

Participants do not appear to agree on the limit's value, as different methods yield different results. The discussion remains unresolved with multiple competing views on the correct approach.

Contextual Notes

There are indications of missing assumptions regarding the methods used, particularly in the transition to polar coordinates and the application of L'Hôpital's Rule. The dependence on specific mathematical techniques may affect the outcomes.

Jamie2
Messages
17
Reaction score
0
View attachment 2085

I got that the limit equals 0 by simplifying the denominator from:

((x2+y2+1)1/2) - 1

to
((x2 - (y+1)(y-1))1/2) - 1

then
((x2 - (y(1+1)(1-1))1/2) - 1

and then evaluating the limit by plugging in 0, getting 0/-1=0

is this correct? is there a better way to do it?
 

Attachments

  • Screen Shot 2014-03-06 at 1.30.14 PM.png
    Screen Shot 2014-03-06 at 1.30.14 PM.png
    2.9 KB · Views: 99
Physics news on Phys.org
I get a different result by converting to polar. This result is confirmed by W|A. So, I suggest using polar coordinates...what do you find?
 
Could you explain in more detail? I don't think I understand what you mean
 
Essentially, I used $x^2+y^2=r^2$ and the limit becomes:

$$\lim_{r\to0}\left(\frac{r^2}{\sqrt{r^2+1}-1} \right)$$

And then I rationalized the denominator. You could also at this point use L'Hôpital's Rule.
 

Similar threads

  • · Replies 12 ·
Replies
12
Views
2K
Replies
3
Views
2K
  • · Replies 29 ·
Replies
29
Views
3K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 4 ·
Replies
4
Views
4K
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K