Math Problem Statement

Evaluate the limit \( \lim_{x \to 0} \left(\frac{1}{x} - \frac{1}{\sin x}\right) = \lim_{x \to 0} \left(\frac{\sin x - x}{x \sin x}\right) \)

Solution

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Problem in the Image:

The problem is:

limx0(1x1sinx)=limx0(sinxxxsinx)\lim_{x \to 0} \left(\frac{1}{x} - \frac{1}{\sin x}\right) = \lim_{x \to 0} \left(\frac{\sin x - x}{x \sin x}\right)

We need to evaluate the limit:

limx0(sinxxxsinx)\lim_{x \to 0} \left(\frac{\sin x - x}{x \sin x}\right)

Solution:

To solve this limit, we can use the Taylor series expansion for sinx\sin x around x=0x = 0:

sinx=xx36+O(x5)\sin x = x - \frac{x^3}{6} + \mathcal{O}(x^5)

So,

sinxx=(xx36+O(x5))x=x36+O(x5)\sin x - x = \left(x - \frac{x^3}{6} + \mathcal{O}(x^5)\right) - x = -\frac{x^3}{6} + \mathcal{O}(x^5)

Substituting this into the limit:

limx0(sinxxxsinx)=limx0x36+O(x5)x(xx36+O(x5))\lim_{x \to 0} \left(\frac{\sin x - x}{x \sin x}\right) = \lim_{x \to 0} \frac{-\frac{x^3}{6} + \mathcal{O}(x^5)}{x \left(x - \frac{x^3}{6} + \mathcal{O}(x^5)\right)}

Simplifying the denominator:

xsinx=x(xx36+O(x5))=x2x46+O(x6)x \sin x = x \left(x - \frac{x^3}{6} + \mathcal{O}(x^5)\right) = x^2 - \frac{x^4}{6} + \mathcal{O}(x^6)

Now the limit becomes:

limx0x36x2x46\lim_{x \to 0} \frac{-\frac{x^3}{6}}{x^2 - \frac{x^4}{6}}

Further simplification gives:

limx0x36x2(1x26)=limx0x36x211x26=limx0x61x26\lim_{x \to 0} \frac{-\frac{x^3}{6}}{x^2 \left(1 - \frac{x^2}{6}\right)} = \lim_{x \to 0} \frac{-\frac{x^3}{6}}{x^2} \cdot \frac{1}{1 - \frac{x^2}{6}} = \lim_{x \to 0} \frac{-\frac{x}{6}}{1 - \frac{x^2}{6}}

As x0x \to 0, the limit simplifies to:

limx0x6=0\lim_{x \to 0} -\frac{x}{6} = 0

Conclusion:

The limit evaluates to 00.


Do you have any questions or would you like more details on any part of the solution? Here are a few related questions you might consider:

  1. How does the Taylor series help in evaluating limits involving trigonometric functions?
  2. What are the common limits involving sin(x)\sin(x) and how are they derived?
  3. How can L'Hôpital's rule be used to evaluate this limit?
  4. Why does the higher-order term O(x5)\mathcal{O}(x^5) become negligible as x0x \to 0?
  5. What other methods could be used to solve this limit problem?

Tip: When dealing with trigonometric limits, Taylor series expansions can be very useful for simplification and understanding the behavior near a specific point.

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Math Problem Analysis

Mathematical Concepts

Calculus
Limits
Taylor Series

Formulas

\(\lim_{x \to 0} \left(\frac{\sin x - x}{x \sin x}\right)\)
Taylor series for \(\sin x\): \(\sin x = x - \frac{x^3}{6} + \mathcal{O}(x^5)\)

Theorems

Taylor Series Expansion
Limit Theorems

Suitable Grade Level

Grades 11-12