Math Problem Statement

Solve indeterminate form of (tanx/x)^(1/x^3)

Solution

We are tasked with finding the limit of the following expression as xx approaches 0:

(tan(x)x)1x3\left( \frac{\tan(x)}{x} \right)^{\frac{1}{x^3}}

Step 1: Analyzing the indeterminate form

We start by substituting x=0x = 0 into the expression:

(tan(0)0)103\left( \frac{\tan(0)}{0} \right)^{\frac{1}{0^3}}

Since tan(0)=0\tan(0) = 0 and the expression involves division by 0, this clearly leads to an indeterminate form of the type 000^0.

Step 2: Taking the natural logarithm

To handle this indeterminate form, we take the natural logarithm of the entire expression and solve the limit of the logarithm first. Let:

L=limx0(tan(x)x)1x3L = \lim_{x \to 0} \left( \frac{\tan(x)}{x} \right)^{\frac{1}{x^3}}

Then, taking the logarithm of both sides:

lnL=limx01x3ln(tan(x)x)\ln L = \lim_{x \to 0} \frac{1}{x^3} \ln \left( \frac{\tan(x)}{x} \right)

Step 3: Simplifying the expression

Next, we simplify the term inside the logarithm. We know that as x0x \to 0:

tan(x)x1\frac{\tan(x)}{x} \to 1

Thus, ln(tan(x)x)ln(1)=0\ln \left( \frac{\tan(x)}{x} \right) \to \ln(1) = 0. However, we need to explore this more carefully because we have the term 1x3\frac{1}{x^3} multiplying it. To better understand the behavior of ln(tan(x)x)\ln \left( \frac{\tan(x)}{x} \right), we use the approximation for tan(x)\tan(x) near 0:

tan(x)x+x33+O(x5)\tan(x) \approx x + \frac{x^3}{3} + O(x^5)

So,

tan(x)x1+x23\frac{\tan(x)}{x} \approx 1 + \frac{x^2}{3}

Now, applying the logarithmic approximation for small xx:

ln(1+x23)x23\ln \left( 1 + \frac{x^2}{3} \right) \approx \frac{x^2}{3}

Step 4: Substituting the approximation

Substitute this approximation into the limit:

lnL=limx01x3x23=limx0x23x3=limx013x\ln L = \lim_{x \to 0} \frac{1}{x^3} \cdot \frac{x^2}{3} = \lim_{x \to 0} \frac{x^2}{3x^3} = \lim_{x \to 0} \frac{1}{3x}

As x0x \to 0, 13x\frac{1}{3x} \to \infty. Therefore:

lnL\ln L \to -\infty

Step 5: Final conclusion

Since lnL\ln L \to -\infty, it follows that:

L=e=0L = e^{-\infty} = 0

Thus, the original limit is:

limx0(tan(x)x)1x3=0\lim_{x \to 0} \left( \frac{\tan(x)}{x} \right)^{\frac{1}{x^3}} = 0

Conclusion:

The limit of (tan(x)x)1x3\left( \frac{\tan(x)}{x} \right)^{\frac{1}{x^3}} as xx approaches 0 is 00.


Do you need further details or explanations on any step? Here are some related questions you could explore:

  1. How does the approximation tan(x)x+x33\tan(x) \approx x + \frac{x^3}{3} work for small xx?
  2. What other indeterminate forms can arise in calculus?
  3. How can L'Hopital's Rule help in solving limits involving indeterminate forms?
  4. What is the significance of the natural logarithm in handling limits of powers?
  5. Can you generalize this result for other trigonometric functions?

Tip: Always check the indeterminate form type before applying logarithmic techniques.

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Math Problem Analysis

Mathematical Concepts

Limits
Indeterminate Forms
Logarithms
Trigonometry

Formulas

Limit definition: \( \lim_{x \to 0} \)
Trigonometric approximation: \( \tan(x) \approx x + \frac{x^3}{3} \)
Logarithmic approximation: \( \ln(1 + x) \approx x \text{ for small } x \)

Theorems

Indeterminate Form \( 0^0 \)
L'Hopital's Rule (implicit in solving limits)

Suitable Grade Level

Advanced High School or Early College (Grades 11-12, Calculus Level)