Solving Trigonometric Limit w/o L'Hospital Rule

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SUMMARY

The forum discussion focuses on solving the limit $\lim_{x\to1}\frac{\sin(x^{3}-1)}{x-1}$ without using L'Hôpital's rule. Participants suggest multiplying the numerator and denominator by $x^{2} + x + 1$ to simplify the expression. The key insight is recognizing that $\lim_{x \rightarrow 1} \frac{\sin (x^{3}-1)}{x^{3}-1} = 1$ and $\lim_{x \rightarrow 1} (x^{2} + x + 1) = 3$, leading to the final result of 3. This method effectively circumvents the need for L'Hôpital's rule while providing a clear path to the solution.

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Yankel
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Hello,

I need some help with this limit, I have no clue how to do this with the next constraint: No use of L'hopital rule...

Thank you !

\lim_{x\to1}\frac{sin(x^{3}-1)}{x-1}
 
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Yankel said:
Hello,

I need some help with this limit, I have no clue how to do this with the next constraint: No use of L'hopital rule...

Thank you !

\lim_{x\to1}\frac{sin(x^{3}-1)}{x-1}

Try multiplying numerator and denominator by $x^{2} + x + 1$...

Kind regards

$\chi$ $\sigma$
 
chisigma said:
Try multiplying numerator and denominator by $x^{2} + x + 1$...

Kind regards

$\chi$ $\sigma$

I thought about it, it gives me what's in the sine, however x->1 and not x->0, so I am still stuck...
 
Yankel said:
I thought about it, it gives me what's in the sine, however x->1 and not x->0, so I am still stuck...

$\displaystyle \lim_{x \rightarrow 1} \frac{\sin (x^{3}-1)}{x-1} = \lim_{x \rightarrow 1} \frac{\sin (x^{3}-1)}{x^{3}-1}\ (x^{2} + x + 1)$

... and now what is $\displaystyle \lim_{x \rightarrow 1} \frac{\sin (x^{3}-1)}{x^{3}-1}$?...

... and what is $\displaystyle \lim_{x \rightarrow 1} x^{2} + x + 1$?...

Kind regards

$\chi$ $\sigma$
 
Also, L'Hôpital's rule allows us to write:

$\displaystyle \lim_{x\to1}\frac{\sin(x^3-1)}{x-1}=3\lim_{x\to1}x^2\cos(x^3-1)$
 

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