Math Problem Statement

Evaluate the limit: lim (x → 1⁺) (1 / √(x - 1) - 1 / √(x² - 1))

Solution

The given limit problem is:

limx1+(1x11x21)\lim_{{x \to 1^+}} \left( \frac{1}{\sqrt{x-1}} - \frac{1}{\sqrt{x^2-1}} \right)

Let's analyze the limit step by step.

  1. Simplification of the second term: The expression inside the second square root is x21x^2 - 1, which can be factored: x21=(x1)(x+1)x^2 - 1 = (x - 1)(x + 1) Thus, the second term becomes: 1x21=1(x1)(x+1)=1x1x+1\frac{1}{\sqrt{x^2 - 1}} = \frac{1}{\sqrt{(x-1)(x+1)}} = \frac{1}{\sqrt{x-1} \cdot \sqrt{x+1}}

  2. Rewrite the original expression: Substituting this into the original limit, we have: limx1+(1x11x1x+1)\lim_{{x \to 1^+}} \left( \frac{1}{\sqrt{x-1}} - \frac{1}{\sqrt{x-1} \cdot \sqrt{x+1}} \right)

  3. Factor out 1x1\frac{1}{\sqrt{x-1}}: limx1+1x1(11x+1)\lim_{{x \to 1^+}} \frac{1}{\sqrt{x-1}} \left( 1 - \frac{1}{\sqrt{x+1}} \right)

  4. Examine the limit as x1+x \to 1^+:

    • As x1+x \to 1^+, x10+\sqrt{x - 1} \to 0^+.
    • x+12\sqrt{x+1} \to \sqrt{2}.

    So, the expression becomes: limx1+10+(112)\lim_{{x \to 1^+}} \frac{1}{0^+} \left( 1 - \frac{1}{\sqrt{2}} \right) The term inside the parentheses approaches a constant value: 112=12210.7071=0.29291 - \frac{1}{\sqrt{2}} = 1 - \frac{\sqrt{2}}{2} \approx 1 - 0.7071 = 0.2929

  5. Conclusion: The expression simplifies to: 10+0.2929\frac{1}{0^+} \cdot 0.2929 Since 10+\frac{1}{0^+} tends to infinity, the overall limit tends to infinity. Therefore:

\boxed{\infty}

The limit as xx approaches 1 from the right is infinity.

Would you like more details on any step or have further questions?

Here are some related questions:

  1. How do you factor and simplify expressions like x21x^2 - 1?
  2. What is the meaning of x1+x \to 1^+ in limit problems?
  3. How does multiplying by 10+\frac{1}{0^+} lead to infinity?
  4. How do square roots affect limit behavior near boundary points?
  5. What strategies can simplify expressions involving square roots?

Tip: In limits involving indeterminate forms or complex expressions, factoring and cancellation often help to simplify the problem!

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Math Problem Analysis

Mathematical Concepts

Limits
Algebra
Square Roots
Indeterminate Forms

Formulas

Difference of squares: x² - 1 = (x - 1)(x + 1)
Simplification of radicals

Theorems

Properties of limits
Behavior of functions near boundary points

Suitable Grade Level

Grades 11-12