Math Problem Statement

Limite lorsque x tend vers moins l'infinie

lim_{x \to -\infty} \frac{\sqrt{x^2 + x + 1}}{x - 2}

Solution

We are asked to find the limit:

limxx2+x+1x2\lim_{x \to -\infty} \frac{\sqrt{x^2 + x + 1}}{x - 2}

Step-by-Step Solution:

  1. Behavior of the Square Root: As xx \to -\infty, the dominant term inside the square root is x2x^2, so we can factor out x2x^2 from the expression under the square root:

    = |x| \sqrt{1 + \frac{1}{x} + \frac{1}{x^2}}.$$ Since $$x \to -\infty$$, $$|x| = -x$$, so: $$\sqrt{x^2 + x + 1} \approx -x \sqrt{1 + \frac{1}{x} + \frac{1}{x^2}}.$$ As $$x \to -\infty$$, both $$\frac{1}{x}$$ and $$\frac{1}{x^2}$$ approach zero, so: $$\sqrt{x^2 + x + 1} \approx -x.$$
  2. Simplifying the Limit Expression: Now, substitute this approximation into the limit expression:

    x2+x+1x2xx2.\frac{\sqrt{x^2 + x + 1}}{x - 2} \approx \frac{-x}{x - 2}.

  3. Final Simplification: Divide both the numerator and denominator by xx:

    xx2=xx(12x)=112x.\frac{-x}{x - 2} = \frac{-x}{x(1 - \frac{2}{x})} = \frac{-1}{1 - \frac{2}{x}}.

    As xx \to -\infty, 2x0\frac{2}{x} \to 0, so:

    110=1.\frac{-1}{1 - 0} = -1.

Final Answer:

limxx2+x+1x2=1.\lim_{x \to -\infty} \frac{\sqrt{x^2 + x + 1}}{x - 2} = -1.


Would you like further details or clarifications?

Here are some related questions to explore:

  1. How would the limit change if x+x \to +\infty?
  2. What happens if we replace x2x^2 with a higher degree polynomial?
  3. What is the geometric interpretation of this limit?
  4. How does the behavior of the function differ near x=2x = 2?
  5. Can L'Hopital's Rule be applied in this case?

Tip: When dealing with limits involving square roots, always factor out the highest power of xx from inside the square root to simplify the expression.

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Math Problem Analysis

Mathematical Concepts

Limits
Asymptotic Behavior
Square Root Simplification

Formulas

\lim_{x \to -\infty} \frac{\sqrt{x^2 + x + 1}}{x - 2}
|x| = -x for x \to -\infty

Theorems

Behavior of Polynomials at Infinity

Suitable Grade Level

Grades 10-12 (High School/Advanced)