Math Problem Statement

Find the limit lim_{x -> 2} [(3x - 1)^3 - (x + 3)^3] / (x^3 - 8).

Solution

The problem in the image deals with finding the limit of the expression limx2(3x1)3(x+3)3x38\lim_{x \to 2} \frac{(3x - 1)^3 - (x + 3)^3}{x^3 - 8}.

Solution breakdown:

  1. Direct substitution:

    • First, the solution substitutes x=2x = 2 into the expression, leading to the form 00\frac{0}{0}, which is indeterminate. This indicates that a different approach is needed to evaluate the limit.
  2. Factoring the numerator:

    • The solution proceeds by factoring the cubic expressions in the numerator.
    • Both (3x1)3(3x - 1)^3 and (x+3)3(x + 3)^3 are expanded and simplified.
    • After factoring out common terms, the numerator can be expressed in a factored form that cancels out the indeterminate part with the denominator.
  3. Simplifying:

    • The factor (x2)(x - 2) is factored out of the numerator and cancels with the corresponding factor in the denominator, leaving a simpler expression to substitute x=2x = 2.
  4. Final substitution:

    • After canceling and simplifying, the limit can be evaluated by direct substitution, which yields the final result 252\frac{25}{2}.

Thus, the final answer is:

limx2(3x1)3(x+3)3x38=252\lim_{x \to 2} \frac{(3x - 1)^3 - (x + 3)^3}{x^3 - 8} = \frac{25}{2}


Would you like more details on any step?

Here are 5 questions to expand your understanding:

  1. Why is it necessary to factor the expression when the direct substitution gives 00\frac{0}{0}?
  2. How is the difference of cubes formula used in this problem?
  3. What are the steps to expand (3x1)3(3x - 1)^3 and (x+3)3(x + 3)^3?
  4. How do we factor out the common terms from the numerator and denominator?
  5. What would happen if we used L'Hopital's Rule instead of factoring?

Tip: When facing indeterminate forms like 00\frac{0}{0}, look for factoring or simplifying techniques to resolve the limit.

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Math Problem Analysis

Mathematical Concepts

Limits
Factoring
Algebraic Simplification

Formulas

Difference of cubes: a^3 - b^3 = (a - b)(a^2 + ab + b^2)

Theorems

Factoring Method
Direct Substitution in Limits

Suitable Grade Level

Grades 11-12