Math Problem Statement

Evaluate the limit as x approaches 3 of the expression: A = lim_{x→3} (3(x^2 - 9)(x^2 + 7)) / (x^2 - 2x).

Solution

The problem from the image reads as follows:

A=limx33(x29)(x2+7)(x22x).A = \lim_{x \to 3} \frac{3(x^2 - 9)(x^2 + 7)}{(x^2 - 2x)}.

Step-by-Step Solution:

  1. Simplify the numerator:

    • The numerator is 3(x29)(x2+7)3(x^2 - 9)(x^2 + 7).
    • Notice that x29x^2 - 9 can be factored as: x29=(x3)(x+3).x^2 - 9 = (x - 3)(x + 3).
    • So, the numerator becomes: 3(x3)(x+3)(x2+7).3(x - 3)(x + 3)(x^2 + 7).
  2. Simplify the denominator:

    • The denominator is x22xx^2 - 2x.
    • Factor out xx from x22xx^2 - 2x: x22x=x(x2).x^2 - 2x = x(x - 2).
  3. Substitute the factored forms:

    • Rewrite the expression: A=limx33(x3)(x+3)(x2+7)x(x2).A = \lim_{x \to 3} \frac{3(x - 3)(x + 3)(x^2 + 7)}{x(x - 2)}.
  4. Handle the indeterminate form:

    • If we substitute x=3x = 3 directly, the term x3x - 3 in the numerator becomes 00, leading to a division by zero. This means the limit results in an indeterminate form, so we need to simplify further.
  5. Cancel out the common factor x3x - 3:

    • The term x3x - 3 is common in the numerator and denominator. Cancel it out (noting that x3x \neq 3 while taking the limit): A=limx33(x+3)(x2+7)x(x2).A = \lim_{x \to 3} \frac{3(x + 3)(x^2 + 7)}{x(x - 2)}.
  6. Substitute x=3x = 3:

    • After cancellation, substitute x=3x = 3 into the simplified expression: A=3((3)+3)((3)2+7)(3)((3)2).A = \frac{3((3) + 3)((3)^2 + 7)}{(3)((3) - 2)}.
    • Simplify each term:
      • 3+3=63 + 3 = 6,
      • 32+7=9+7=163^2 + 7 = 9 + 7 = 16,
      • 32=13 - 2 = 1.
    • Substitute these values: A=3(6)(16)3(1).A = \frac{3(6)(16)}{3(1)}.
  7. Simplify the final expression:

    • The factor 33 cancels out from the numerator and denominator: A=616=96.A = 6 \cdot 16 = 96.

Final Answer:

A=96.A = 96.

Would you like further clarification or additional details?


5 Related Questions:

  1. What are some techniques to evaluate limits involving indeterminate forms?
  2. How can factoring simplify limits involving polynomials?
  3. What is L'Hôpital's Rule, and when is it applicable?
  4. Can you explain why we cancel terms like x3x - 3 in limits even though x=3x = 3 is undefined?
  5. How do we interpret the meaning of limits in calculus?

Tip:

Always check for common factors to simplify a limit before applying other techniques, as it often avoids unnecessary complexity!

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Math Problem Analysis

Mathematical Concepts

Limits
Factoring Polynomials
Simplifying Expressions

Formulas

Limit as x → a
Factoring: a^2 - b^2 = (a - b)(a + b)

Theorems

Limit Laws
Polynomial Factoring Rules

Suitable Grade Level

Grade 11-12 or early college-level calculus