Math Problem Statement

Evaluate lim (x → ∞) √((3x^3 + 5x - 1)^3 (9 - 2x^2)^2 / ((2x + 7)(4x^4 - 5)^3))

Solution

The given expression asks to evaluate the limit as xx \to \infty of the following function:

limx(3x3+5x1)3(92x2)2(2x+7)(4x45)3\lim_{x \to \infty} \sqrt{\frac{(3x^3 + 5x - 1)^3 (9 - 2x^2)^2}{(2x + 7) (4x^4 - 5)^3}}

Step-by-step breakdown:

  1. Analyze the asymptotic behavior:

    • As xx \to \infty, we focus on the highest degree terms in both the numerator and denominator, since those will dominate the behavior of the expression.

    • Numerator:

      • 3x3+5x13x33x^3 + 5x - 1 \sim 3x^3
      • 92x22x29 - 2x^2 \sim -2x^2 Therefore, the numerator behaves like: (3x3)3(2x2)2=27x94x4=108x13(3x^3)^3 (-2x^2)^2 = 27x^9 \cdot 4x^4 = 108x^{13}
    • Denominator:

      • 2x+72x2x + 7 \sim 2x
      • 4x454x44x^4 - 5 \sim 4x^4 Therefore, the denominator behaves like: 2x(4x4)3=2x64x12=128x132x \cdot (4x^4)^3 = 2x \cdot 64x^{12} = 128x^{13}
  2. Simplify the asymptotic limit: So, the expression inside the square root becomes asymptotically: 108x13128x13=108128=2732\frac{108x^{13}}{128x^{13}} = \frac{108}{128} = \frac{27}{32}

  3. Take the square root: 2732=2732=3342=368\sqrt{\frac{27}{32}} = \frac{\sqrt{27}}{\sqrt{32}} = \frac{3\sqrt{3}}{4\sqrt{2}} = \frac{3\sqrt{6}}{8}

Thus, the value of the limit is:

368\boxed{\frac{3\sqrt{6}}{8}}

Let me know if you would like further details on any of the steps!

Related questions:

  1. How would the solution change if the degree of the polynomial in the numerator was higher?
  2. What happens to the limit if the denominator had an additional higher-degree term?
  3. How can you determine the dominant term for complex functions as xx \to \infty?
  4. Can L'Hopital's Rule be applied to this type of limit problem?
  5. What is the behavior of this function as xx \to -\infty?

Tip:

When evaluating limits at infinity, always focus on the highest power terms, as they dominate the behavior of the function.

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Math Problem Analysis

Mathematical Concepts

Limits
Asymptotic Behavior
Polynomial Division

Formulas

Asymptotic approximation: lim(x → ∞) P(x)/Q(x) ≈ highest degree terms
Square root simplification
Limit of a ratio of polynomials

Theorems

Limits at infinity
Polynomials leading term dominance

Suitable Grade Level

University/Advanced Calculus