Math Problem Statement

Evaluate the limit: lim (x → ∞) (sqrt(8x^2 + 5x - 7) / sqrt(2x^2 + 3x - 1)).

Solution

We are given the following limit problem:

limx8x2+5x72x2+3x1\lim_{{x \to \infty}} \frac{\sqrt{8x^2 + 5x - 7}}{\sqrt{2x^2 + 3x - 1}}

Step-by-step solution:

  1. Simplifying the square roots: Since both the numerator and the denominator involve square roots of quadratic expressions, we can factor out x2x^2 from inside the square roots.

    • In the numerator: 8x2+5x7=x2(8+5x7x2)=x8+5x7x2\sqrt{8x^2 + 5x - 7} = \sqrt{x^2 \left( 8 + \frac{5}{x} - \frac{7}{x^2} \right)} = |x| \sqrt{8 + \frac{5}{x} - \frac{7}{x^2}} As xx \to \infty, we can drop the absolute value of xx because xx is positive in this limit.

    • In the denominator: 2x2+3x1=x2(2+3x1x2)=x2+3x1x2\sqrt{2x^2 + 3x - 1} = \sqrt{x^2 \left( 2 + \frac{3}{x} - \frac{1}{x^2} \right)} = |x| \sqrt{2 + \frac{3}{x} - \frac{1}{x^2}} Again, as xx \to \infty, we drop the absolute value.

  2. Taking the limit as xx \to \infty: As xx \to \infty, the terms 5x\frac{5}{x}, 7x2\frac{7}{x^2}, 3x\frac{3}{x}, and 1x2\frac{1}{x^2} all approach 0. So, the expressions simplify to:

    • Numerator: 8+0+0=8\sqrt{8 + 0 + 0} = \sqrt{8}
    • Denominator: 2+0+0=2\sqrt{2 + 0 + 0} = \sqrt{2}
  3. Final limit expression: The limit becomes: limx82=82=222=2\lim_{{x \to \infty}} \frac{\sqrt{8}}{\sqrt{2}} = \frac{\sqrt{8}}{\sqrt{2}} = \frac{2\sqrt{2}}{\sqrt{2}} = 2

Thus, the value of the limit is 2\boxed{2}.

Would you like more details or have any further questions?

Here are 5 related questions for deeper understanding:

  1. What happens to the limit if the degree of the polynomial in the numerator is higher than in the denominator?
  2. How do you approach limits where the terms inside the square roots grow faster than quadratic terms?
  3. Can you find the limit if the expression involves cube roots instead of square roots?
  4. What if we were finding the limit as xx \to -\infty instead?
  5. How would the limit change if one of the coefficients inside the square root was negative?

Tip: When evaluating limits of square roots of polynomials as xx \to \infty, always factor out the highest power of xx from under the square root to simplify.

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Math Problem Analysis

Mathematical Concepts

Limits
Square roots
Rational functions
Algebra

Formulas

lim (x → ∞) (sqrt(ax^2 + bx + c) / sqrt(dx^2 + ex + f))
Simplifying expressions involving limits by factoring

Theorems

Limit Laws
Properties of square roots

Suitable Grade Level

Grades 11-12