Math Problem Statement

lim (x -> 3) (2x^2 + 4x - 5) / (x^2 - 5x + 6)

Solution

The limit problem you provided is:

limx32x2+4x5x25x+6\lim_{{x \to 3}} \frac{2x^2 + 4x - 5}{x^2 - 5x + 6}

Step-by-Step Solution:

  1. Check for direct substitution: Substitute x=3x = 3 directly into the expression.

    Numerator: 2(3)2+4(3)5=18+125=25\text{Numerator: } 2(3)^2 + 4(3) - 5 = 18 + 12 - 5 = 25 Denominator: (3)25(3)+6=915+6=0\text{Denominator: } (3)^2 - 5(3) + 6 = 9 - 15 + 6 = 0

    Since the denominator is 0 and the numerator is 25, this results in a form of 250\frac{25}{0}, indicating that the limit does not exist in the conventional sense. However, we can explore whether it tends to \infty or -\infty by analyzing the behavior near x=3x = 3.

  2. Factor the denominator: Factor the quadratic expression in the denominator.

    x25x+6=(x2)(x3)x^2 - 5x + 6 = (x - 2)(x - 3)

  3. Analyze the behavior near x=3x = 3: We now have:

    2x2+4x5(x2)(x3)\frac{2x^2 + 4x - 5}{(x - 2)(x - 3)}

    As x3x \to 3, the factor (x3)(x - 3) in the denominator approaches 0, which causes the whole expression to blow up. To determine the sign of the limit, we examine the behavior from the left (x3x \to 3^-) and from the right (x3+x \to 3^+).

    • As x3x \to 3^- (approaching from the left), (x3)(x - 3) is negative, and the rest of the expression remains positive, so the limit tends to -\infty.
    • As x3+x \to 3^+ (approaching from the right), (x3)(x - 3) is positive, and the rest of the expression remains positive, so the limit tends to ++\infty.
  4. Conclusion: Since the limit approaches -\infty from the left and ++\infty from the right, the limit does not exist.

Final Answer:

limx32x2+4x5x25x+6=does not exist (DNE)\lim_{{x \to 3}} \frac{2x^2 + 4x - 5}{x^2 - 5x + 6} = \text{does not exist (DNE)}

Would you like more details on this or have any other questions? Here are some related questions for further exploration:

  1. How do you determine whether a limit approaches infinity or negative infinity?
  2. What is the significance of factoring when solving limits involving rational functions?
  3. What does it mean when a limit does not exist in terms of real-world applications?
  4. How can L'Hôpital's Rule be applied in limit problems with indeterminate forms?
  5. What are the conditions for applying L'Hôpital's Rule?

Tip: When solving limits with rational functions, always try direct substitution first to identify potential indeterminate forms. Then factor the expression to simplify further.

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Math Problem Analysis

Mathematical Concepts

Limits
Rational Functions
Factoring

Formulas

Factorization of quadratic equations
Limit calculation methods

Theorems

Limit Theorem for Rational Functions
Zero in the denominator causing discontinuity

Suitable Grade Level

Grades 11-12