Math Problem Statement

A function is said to have a vertical asymptote wherever the limit on the left or right (or both) is either positive or negative infinity. For example, the function f(x)=−3(x+2)x2+4x+4 has a vertical asymptote at x=−2. Find each of the following limits. limx→−2−−3(x+2)x2+4x+4= help (limits)

limx→−2+−3(x+2)x2+4x+4= help (limits)

limx→−2−3(x+2)x2+4x+4= help (limits)

Solution

Let's analyze the limits of the given function f(x)=3(x+2)x2+4x+4f(x) = -\frac{3(x+2)}{x^2 + 4x + 4} at x=2x = -2.

The function has a vertical asymptote at x=2x = -2. This is because the denominator x2+4x+4x^2 + 4x + 4 becomes 0 when x=2x = -2. To find each limit, we'll evaluate the behavior of the function from both the left-hand side (x2x \to -2^-) and the right-hand side (x2+x \to -2^+).

1. Limit from the left limx2(3(x+2)x2+4x+4)\lim_{x \to -2^-} \left( -\frac{3(x+2)}{x^2 + 4x + 4} \right)

The denominator is x2+4x+4=(x+2)2x^2 + 4x + 4 = (x + 2)^2. At x=2x = -2, this denominator is 0 because (x+2)2=0(x + 2)^2 = 0. Since the denominator is squared, it will always be positive as we approach x=2x = -2 from either side, but the numerator depends on the behavior of x+2x + 2.

  • As x2x \to -2^-, the term x+2x + 2 becomes a small negative number (just slightly less than 0).
  • Therefore, 3(x+2)-3(x+2) becomes a small positive number (since the negative of a negative is positive).

Hence, as x2x \to -2^-, the function behaves like:

limx23(x+2)(x+2)2positive small numberpositive small number+\lim_{x \to -2^-} -\frac{3(x+2)}{(x+2)^2} \approx \frac{\text{positive small number}}{\text{positive small number}} \to +\infty

Thus:

limx2(3(x+2)x2+4x+4)=+\lim_{x \to -2^-} \left( -\frac{3(x+2)}{x^2 + 4x + 4} \right) = +\infty

2. Limit from the right limx2+(3(x+2)x2+4x+4)\lim_{x \to -2^+} \left( -\frac{3(x+2)}{x^2 + 4x + 4} \right)

Now, let's approach x=2x = -2 from the right-hand side (x2+x \to -2^+).

  • As x2+x \to -2^+, the term x+2x + 2 becomes a small positive number (just slightly greater than 0).
  • Therefore, 3(x+2)-3(x+2) becomes a small negative number.

Thus, as x2+x \to -2^+, the function behaves like:

limx2+3(x+2)(x+2)2negative small numberpositive small number\lim_{x \to -2^+} -\frac{3(x+2)}{(x+2)^2} \approx \frac{\text{negative small number}}{\text{positive small number}} \to -\infty

Therefore:

limx2+(3(x+2)x2+4x+4)=\lim_{x \to -2^+} \left( -\frac{3(x+2)}{x^2 + 4x + 4} \right) = -\infty

3. Two-sided limit limx2(3(x+2)x2+4x+4)\lim_{x \to -2} \left( -\frac{3(x+2)}{x^2 + 4x + 4} \right)

Since the left-hand limit and right-hand limit as x2x \to -2 do not match (one approaches ++\infty and the other approaches -\infty), the two-sided limit does not exist.

Thus:

limx2(3(x+2)x2+4x+4)=does not exist\lim_{x \to -2} \left( -\frac{3(x+2)}{x^2 + 4x + 4} \right) = \text{does not exist}


Summary:

  1. limx2(3(x+2)x2+4x+4)=+\lim_{x \to -2^-} \left( -\frac{3(x+2)}{x^2 + 4x + 4} \right) = +\infty
  2. limx2+(3(x+2)x2+4x+4)=\lim_{x \to -2^+} \left( -\frac{3(x+2)}{x^2 + 4x + 4} \right) = -\infty
  3. limx2(3(x+2)x2+4x+4)=does not exist\lim_{x \to -2} \left( -\frac{3(x+2)}{x^2 + 4x + 4} \right) = \text{does not exist}

Would you like further clarification or details on any of these steps?

Related Questions:

  1. How do vertical asymptotes affect the graph of a rational function?
  2. Can a function have more than one vertical asymptote?
  3. What is the difference between vertical and horizontal asymptotes?
  4. How do you find horizontal asymptotes of a rational function?
  5. What is the behavior of a function near a hole versus an asymptote?

Tip:

When dealing with rational functions, always factor the denominator and numerator completely to help locate vertical asymptotes and simplify limits.

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Math Problem Analysis

Mathematical Concepts

Limits
Rational Functions
Asymptotes
Infinity in Limits

Formulas

lim x→a f(x)
Vertical asymptote criteria (denominator approaching zero)

Theorems

Limits and Asymptotes
Behavior of Rational Functions near Vertical Asymptotes

Suitable Grade Level

Grades 10-12