Math Problem Statement

Evaluate \( \lim_{x \to -1} \left( x^2 \right)^{\frac{1}{1 - x^2}} \).

Solution

The limit in the image is:

limx1(x2)11x2.\lim_{x \to -1} \left( x^2 \right)^{\frac{1}{1 - x^2}}.

Solution Steps:

We analyze the limit step-by-step:

  1. Simplify the base x2x^2:

    • As x1x \to -1, the square of xx is x2(1)2=1x^2 \to (-1)^2 = 1. Therefore, the base approaches 11.
  2. Analyze the exponent 11x2\frac{1}{1 - x^2}:

    • As x1x \to -1, x21x^2 \to 1, so 1x211=01 - x^2 \to 1 - 1 = 0.
    • This makes the denominator 1x201 - x^2 \to 0, which implies the exponent 11x2\frac{1}{1 - x^2} \to \infty (positive infinity).
  3. Form of the limit:

    • The expression now has the form: 1.1^{\infty}.
    • This is an indeterminate form, so we take the natural logarithm to simplify.

Natural Logarithm Approach:

Let L=limx1(x2)11x2L = \lim_{x \to -1} \left( x^2 \right)^{\frac{1}{1 - x^2}}.

Take the natural logarithm on both sides: lnL=limx1ln(x2)1x2.\ln L = \lim_{x \to -1} \frac{\ln (x^2)}{1 - x^2}.

Step-by-step Analysis of the Logarithm:

  • Numerator: ln(x2)=2lnx\ln (x^2) = 2 \ln |x| because ln(ab)=blna\ln (a^b) = b \ln a.

    • As x1x \to -1, lnx=ln1=0\ln |x| = \ln 1 = 0, so ln(x2)0\ln (x^2) \to 0.
  • Denominator: 1x201 - x^2 \to 0 as x1x \to -1.

Thus, we have a fraction of the form 00\frac{0}{0}, so we apply L'Hôpital's Rule.


Applying L'Hôpital's Rule:

Differentiate the numerator and denominator with respect to xx:

  • Derivative of the numerator ln(x2)\ln (x^2): ddxln(x2)=2x.\frac{d}{dx} \ln (x^2) = \frac{2}{x}.

  • Derivative of the denominator 1x21 - x^2: ddx(1x2)=2x.\frac{d}{dx} (1 - x^2) = -2x.

Now apply L'Hôpital's Rule: lnL=limx1ln(x2)1x2=limx12x2x.\ln L = \lim_{x \to -1} \frac{\ln (x^2)}{1 - x^2} = \lim_{x \to -1} \frac{\frac{2}{x}}{-2x}.

Simplify: lnL=limx122x2.\ln L = \lim_{x \to -1} \frac{2}{-2x^2}.

As x1x \to -1, x21x^2 \to 1, so: lnL=221=1.\ln L = \frac{2}{-2 \cdot 1} = -1.


Exponentiate to Solve for LL:

We have lnL=1\ln L = -1, so exponentiate both sides: L=e1.L = e^{-1}.

Thus, the value of the limit is: limx1(x2)11x2=1e.\lim_{x \to -1} \left( x^2 \right)^{\frac{1}{1 - x^2}} = \frac{1}{e}.


Final Answer:

1e\boxed{\frac{1}{e}}

Let me know if you would like any further clarifications or additional steps!


Related Questions:

  1. How do you handle 11^\infty indeterminate forms using logarithms?
  2. What are the steps for applying L'Hôpital's Rule in limits?
  3. How do you differentiate logarithmic functions like ln(x2)\ln(x^2)?
  4. Why does exponentiating both sides help solve limits involving logs?
  5. What other forms of indeterminate limits exist, and how are they resolved?

Tip: When solving 11^\infty forms, always use the logarithm to convert the problem into a solvable fraction!

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Math Problem Analysis

Mathematical Concepts

Limits
Indeterminate Forms
Logarithmic Limits
L'Hôpital's Rule

Formulas

Natural Logarithm: \( \ln(a^b) = b \ln(a) \)
L'Hôpital's Rule: \( \lim_{x \to c} \frac{f(x)}{g(x)} = \lim_{x \to c} \frac{f'(x)}{g'(x)} \) for \( \frac{0}{0} \) or \( \frac{\infty}{\infty} \)
Exponentiation of Limits: \( \ln L \to e^{\ln L} \)

Theorems

L'Hôpital's Rule
Indeterminate Forms \( 1^\infty \)

Suitable Grade Level

Undergraduate Calculus