Math Problem Statement

What is the limit

Solution

To solve the limit problem given in the image, we have the following expression:

limx7x2+7xx22x63\lim_{{x \to 7}} \frac{x^2 + 7x}{x^2 - 2x - 63}

Step 1: Factor the denominator

First, let's factor the denominator x22x63x^2 - 2x - 63:

The quadratic equation is in the form ax2+bx+cax^2 + bx + c. We need to find two numbers that multiply to 63-63 (the constant term) and add to 2-2 (the coefficient of xx).

The numbers 9-9 and 77 satisfy this condition:

x22x63=(x9)(x+7)x^2 - 2x - 63 = (x - 9)(x + 7)

Step 2: Simplify the expression

The limit now becomes:

limx7x2+7x(x9)(x+7)\lim_{{x \to 7}} \frac{x^2 + 7x}{(x - 9)(x + 7)}

The numerator x2+7xx^2 + 7x can also be factored:

x2+7x=x(x+7)x^2 + 7x = x(x + 7)

So the limit simplifies to:

limx7x(x+7)(x9)(x+7)\lim_{{x \to 7}} \frac{x(x + 7)}{(x - 9)(x + 7)}

Now, we can cancel out the common factor (x+7)(x + 7) in the numerator and denominator:

limx7xx9\lim_{{x \to 7}} \frac{x}{x - 9}

Step 3: Substitute x=7x = 7

Now, substitute x=7x = 7 into the simplified expression:

779=72=72\frac{7}{7 - 9} = \frac{7}{-2} = -\frac{7}{2}

Final Answer

The limit is:

limx7x2+7xx22x63=72\lim_{{x \to 7}} \frac{x^2 + 7x}{x^2 - 2x - 63} = -\frac{7}{2}

Would you like more details or have any questions?

Here are some related questions you might find helpful:

  1. How do you factor quadratic expressions?
  2. What are common limit laws and how do they apply?
  3. What is the significance of canceling out terms in a limit problem?
  4. How do you handle indeterminate forms in limits?
  5. What is L'Hôpital's rule and when can it be applied?

Tip: When solving limits, always check for common factors that can simplify the expression, especially when the direct substitution results in an indeterminate form like 00\frac{0}{0}.

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Math Problem Analysis

Mathematical Concepts

Limits
Quadratic Equations
Factorization

Formulas

Limit definition
Quadratic formula

Theorems

Limit laws

Suitable Grade Level

Grades 11-12