Math Problem Statement

Evaluate the following limits: 1. lim (x -> ∞) [-2x / (14 + 2x)] 2. lim (x -> -∞) [(11x - 14) / (x^3 + 5x - 11)] 3. lim (x -> ∞) [(x^2 - 2x - 3) / (6 - 11x^2)] 4. lim (x -> ∞) [√(x^2 + 2x) / (6 - 12x)] 5. lim (x -> -∞) [√(x^2 + 2x) / (6 - 12x)]

Solution

Let's go through each limit problem step by step. The goal is to evaluate these limits as xx \to \infty or xx \to -\infty.

1. limx2x14+2x\lim_{x \to \infty} \frac{-2x}{14 + 2x}

For large xx, the highest degree term in both the numerator and denominator dominates. We can divide the numerator and denominator by xx:

limx2x14+2x=limx214x+2\lim_{x \to \infty} \frac{-2x}{14 + 2x} = \lim_{x \to \infty} \frac{-2}{\frac{14}{x} + 2}

As xx \to \infty, 14x0\frac{14}{x} \to 0, so we get:

limx20+2=22=1\lim_{x \to \infty} \frac{-2}{0 + 2} = \frac{-2}{2} = -1

2. limx11x14x3+5x11\lim_{x \to -\infty} \frac{11x - 14}{x^3 + 5x - 11}

Here, we notice that the denominator grows much faster than the numerator since the highest degree term in the denominator is x3x^3. For large negative xx, the cubic term in the denominator will dominate. This results in:

limx11x14x3+5x1111xx3=11x2\lim_{x \to -\infty} \frac{11x - 14}{x^3 + 5x - 11} \approx \frac{11x}{x^3} = \frac{11}{x^2}

As xx \to -\infty, 11x20\frac{11}{x^2} \to 0, so the limit is:

00

3. limxx22x3611x2\lim_{x \to \infty} \frac{x^2 - 2x - 3}{6 - 11x^2}

For large xx, the highest degree term in both the numerator and denominator dominates. We can divide by x2x^2:

limxx22x3611x2=limx12x3x26x211\lim_{x \to \infty} \frac{x^2 - 2x - 3}{6 - 11x^2} = \lim_{x \to \infty} \frac{1 - \frac{2}{x} - \frac{3}{x^2}}{\frac{6}{x^2} - 11}

As xx \to \infty, the terms involving 1x\frac{1}{x} and 1x2\frac{1}{x^2} go to 0, so this simplifies to:

limx1+0011=111=111\lim_{x \to \infty} \frac{1 + 0}{0 - 11} = \frac{1}{-11} = -\frac{1}{11}

4. limxx2+2x612x\lim_{x \to \infty} \frac{\sqrt{x^2 + 2x}}{6 - 12x}

For large xx, x2+2x\sqrt{x^2 + 2x} can be approximated as x2(1+2x)=x1+2x\sqrt{x^2(1 + \frac{2}{x})} = x\sqrt{1 + \frac{2}{x}}. As xx \to \infty, 1+2x1\sqrt{1 + \frac{2}{x}} \to 1, so:

limxx2+2x612xlimxx12x=112=112\lim_{x \to \infty} \frac{\sqrt{x^2 + 2x}}{6 - 12x} \approx \lim_{x \to \infty} \frac{x}{-12x} = \frac{1}{-12} = -\frac{1}{12}

5. limxx2+2x612x\lim_{x \to -\infty} \frac{\sqrt{x^2 + 2x}}{6 - 12x}

Similar to the previous limit, but now as xx \to -\infty, we have to consider that x2=x\sqrt{x^2} = -x for negative xx. Therefore:

limxx2+2x612xlimxx12x=112=112\lim_{x \to -\infty} \frac{\sqrt{x^2 + 2x}}{6 - 12x} \approx \lim_{x \to -\infty} \frac{-x}{-12x} = \frac{-1}{-12} = \frac{1}{12}

Summary of Limits:

  1. 1-1
  2. 00
  3. 111-\frac{1}{11}
  4. 112-\frac{1}{12}
  5. 112\frac{1}{12}

Do you have any questions or need further clarification on any of these steps?

Here are some additional problems related to limits:

  1. What is the limit limx3x24xx2+5x+6\lim_{x \to \infty} \frac{3x^2 - 4x}{x^2 + 5x + 6}?
  2. How do you evaluate limx7x3+4xx49\lim_{x \to -\infty} \frac{7x^3 + 4x}{x^4 - 9}?
  3. What is the behavior of rational functions at vertical asymptotes?
  4. Evaluate limx01x\lim_{x \to 0} \frac{1}{x} and explain why the limit doesn't exist.
  5. Explore the limit limxex\lim_{x \to \infty} e^{-x} and discuss its real-world applications.

Tip: Always check the highest degree terms in both the numerator and denominator for limits at infinity, as they often dominate the behavior of the function.

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Math Problem Analysis

Mathematical Concepts

Calculus
Limits
Asymptotic Behavior
Simplification of Rational Functions

Formulas

lim (x -> ∞) f(x) / g(x) = lim (x -> ∞) [highest degree terms in f(x) and g(x)]
lim (x -> ∞) √(x^2 + ax) ≈ x

Theorems

Limit Laws
Dominant Term Behavior for Polynomials
Square Root Approximation for Large x

Suitable Grade Level

Undergraduate Calculus or Advanced High School Calculus