Limit Problem: Solving \lim_{x \to 2} \frac{\tan (2 - \sqrt{2x})}{x^2 - 2x}

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SUMMARY

The limit problem discussed is \lim_{x \to 2} \frac{\tan (2 - \sqrt{2x})}{x^2 - 2x}, which evaluates to - \frac{1}{4}. The solution involves applying L'Hôpital's rule and recognizing the limit \lim_{t \to 0} \frac{\tan t}{t} = 1. Participants confirmed the correctness of the solution and discussed alternative methods, including substitution techniques and the importance of understanding derivatives for applying L'Hôpital's rule effectively.

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  • #31
ok, the first thing to do in order to determine ##\lim_ {x\rightarrow 0} \frac{\sqrt{x}(x-7)}{\sqrt{x}-\sqrt{7}}## is to substitute the value ##0## in the espression ##\frac{\sqrt{x}(x-7)}{\sqrt{x}-\sqrt{7}}## and see what happen ...
 
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  • #32
##\lim_{x \to 0} \frac{\sqrt{x}(x - 7)}{\sqrt{x} - \sqrt{7}}##
##=\frac{\sqrt{0}(0 - 7)}{\sqrt{0} - \sqrt{7}}##
##=\frac{0 (- 7)}{- \sqrt{7}}##
##= 0##

Then what?
 
  • #33
Then the limit is ##0##
 
  • #34
Ssnow said:
All it is correct but not necessary, I suggest you to put ##x=0## in the original limit, there are indefinite forms as ##\frac{0}{0},\frac{\infty}{\infty}, 0\cdot \infty, \infty-\infty## or not ?
In English these are called indeterminate forms.
 
  • #35
gede said:
How to solve this limit?

\lim_{x \to 0} \frac{\sqrt{x} (x - 7)}{\sqrt{x} - \sqrt{7}}

This is what I get:

\lim_{x \to 0} \frac{\sqrt{x} (x - 7)}{\sqrt{x} - \sqrt{7}} \frac{\sqrt{x} + \sqrt{7}}{\sqrt{x} + \sqrt{7}}
= \lim_{x \to 0} \frac{\sqrt{x} (x - 7) (\sqrt{x} + \sqrt{7})}{(x - 7)}
= \lim_{x \to 0} \sqrt{x}(\sqrt{x} + \sqrt{7})

What is the next solution?
The limit on the first line above can be evaluated merely by substituting x = 0. You don't need to any of the work you show on the following lines.
 
  • #36
Mark44 said:
In English these are called indeterminate forms.

Yes sorry, an error in the translation ...
 

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