Math Problem Statement

lim (x→−1) (x^2 + 6x + 5) / (x^2 − 3x − 4)

Solution

The limit problem provided is:

limx1x2+6x+5x23x4\lim_{{x \to -1}} \frac{x^2 + 6x + 5}{x^2 - 3x - 4}

Steps to Solve:

  1. Factorize the numerator and denominator:

    • The numerator: x2+6x+5x^2 + 6x + 5 can be factored as (x+5)(x+1)(x + 5)(x + 1).
    • The denominator: x23x4x^2 - 3x - 4 can be factored as (x4)(x+1)(x - 4)(x + 1).
  2. Rewrite the expression: x2+6x+5x23x4=(x+5)(x+1)(x4)(x+1)\frac{x^2 + 6x + 5}{x^2 - 3x - 4} = \frac{(x + 5)(x + 1)}{(x - 4)(x + 1)}

  3. Cancel out common factors: Since (x+1)(x + 1) appears in both the numerator and the denominator, we can cancel it out: x+5x4,x1\frac{x + 5}{x - 4}, \quad x \neq -1 (The condition x1x \neq -1 comes from the fact that x+1x + 1 was canceled, and at x=1x = -1, the original expression would have been undefined.)

  4. Substitute the limit: Now, substitute x=1x = -1 into the simplified expression: 1+514=45=45\frac{-1 + 5}{-1 - 4} = \frac{4}{-5} = -\frac{4}{5}

Final Answer:

limx1x2+6x+5x23x4=45\lim_{{x \to -1}} \frac{x^2 + 6x + 5}{x^2 - 3x - 4} = -\frac{4}{5}

Let me know if you'd like further explanation!

Related Questions:

  1. How do you factor quadratic expressions effectively?
  2. What happens when you cancel common factors in rational expressions?
  3. How do you determine if a function is undefined at a certain point?
  4. What are common techniques for solving limits algebraically?
  5. What is the significance of continuity in determining limits?

Tip: Always check for common factors to simplify expressions before directly substituting values in limit problems.

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Math Problem Analysis

Mathematical Concepts

Limits
Factoring
Algebra
Simplifying Rational Expressions

Formulas

Factorization of quadratic equations
Limit of a rational function

Theorems

Factorization theorem for polynomials
Limit properties for rational functions

Suitable Grade Level

Grades 11-12 or early college level