MHB Does the Limit Exist? Check to Find Out!

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The discussion revolves around evaluating the limit $$\lim_{(x, y) \rightarrow (0, 0)} \frac{\sin 2x-2x+y}{x^3+y}$$. One participant successfully calculated that $$\lim_{x \rightarrow 0} \frac{\sin 2x-2x}{x^3} = -\frac{4}{3}$$ using L'Hôpital's Rule. However, when approaching the limit along different paths, such as $y=0$ and $y=2x - \sin 2x$, different results are obtained: $- \frac{4}{3}$ and $0$, respectively. This discrepancy suggests that the limit does not exist. The conversation highlights the importance of checking limits along various trajectories to determine their existence.
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Hey! :o

I have found applying De L'Hoptal's Rule that $$\lim_{x \rightarrow 0} \frac{\sin 2x-2x}{x^3}=-\frac{4}{3}$$

Now I am asked whether the limit $$\lim_{(x, y) \rightarrow (0, 0)} \frac{\sin 2x-2x+y}{x^3+y}$$ or not.

How could we check that ?? (Wondering)
 
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mathmari said:
Hey! :o

I have found applying De L'Hoptal's Rule that $$\lim_{x \rightarrow 0} \frac{\sin 2x-2x}{x^3}=-\frac{4}{3}$$

Now I am asked whether the limit $$\lim_{(x, y) \rightarrow (0, 0)} \frac{\sin 2x-2x+y}{x^3+y}$$ or not.

How could we check that ?? (Wondering)

Hi! (Wave)

I would start with checking what the limit is on different lines, say $y=0$ respectively $x=0$. (Thinking)
 
mathmari said:
Hey! :o

I have found applying De L'Hoptal's Rule that $$\lim_{x \rightarrow 0} \frac{\sin 2x-2x}{x^3}=-\frac{4}{3}$$

Now I am asked whether the limit $$\lim_{(x, y) \rightarrow (0, 0)} \frac{\sin 2x-2x+y}{x^3+y}$$ or not.

How could we check that ?? (Wondering)

If $(x,y) \rightarrow (0,0)$ along the trajectory y=0 the limit is $- \frac{4}{3}$ as You have found... if $(x,y) \rightarrow (0,0)$ along the trajectory $y = 2\ x - \sin 2x$ the limit is 0... what do You can conclude?...

Kind regards

$\chi$ $\sigma$
 
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