Math Problem Statement

Determine the limit of the expression (3x - 1)^3 - (x + 3)^3 / (x^3 - 8) as x approaches 2.

Solution

The problem in the image appears to be about determining the limit of the following expression:

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

Solution Steps:

  1. Direct Substitution (Substitusi Langsung):

    • First, substituting x=2x = 2 directly into the expression gives:

    limx2(3(2)1)3(2+3)3238=(5)3(5)388=1251250=00\lim_{{x \to 2}} \frac{(3(2) - 1)^3 - (2 + 3)^3}{2^3 - 8} = \frac{(5)^3 - (5)^3}{8 - 8} = \frac{125 - 125}{0} = \frac{0}{0}

    This results in an indeterminate form 00\frac{0}{0}, so we need to manipulate the expression further.

  2. Factoring the Expression:

    • To resolve the indeterminate form, the expression can be factored.
    • Expanding (3x1)3(3x - 1)^3 and (x+3)3(x + 3)^3 gives:

    (3x1)3=27x327x2+9x1(3x - 1)^3 = 27x^3 - 27x^2 + 9x - 1 (x+3)3=x3+9x2+27x+27(x + 3)^3 = x^3 + 9x^2 + 27x + 27

    So, the numerator becomes:

    (27x327x2+9x1)(x3+9x2+27x+27)=26x336x218x28(27x^3 - 27x^2 + 9x - 1) - (x^3 + 9x^2 + 27x + 27) = 26x^3 - 36x^2 - 18x - 28

    Factoring this expression out of common terms:

    2(x2)(13x2+8x+7)2(x - 2)(13x^2 + 8x + 7)

  3. Simplifying the Denominator:

    • The denominator x38x^3 - 8 can be factored as:

    x38=(x2)(x2+2x+4)x^3 - 8 = (x - 2)(x^2 + 2x + 4)

  4. Canceling Common Terms:

    • Now, we can cancel (x2)(x - 2) from both the numerator and denominator:

    limx22(x2)(13x2+8x+7)(x2)(x2+2x+4)=limx22(13x2+8x+7)x2+2x+4\lim_{{x \to 2}} \frac{2(x - 2)(13x^2 + 8x + 7)}{(x - 2)(x^2 + 2x + 4)} = \lim_{{x \to 2}} \frac{2(13x^2 + 8x + 7)}{x^2 + 2x + 4}

  5. Substitute x=2x = 2 Again:

    • Now, substitute x=2x = 2 into the simplified expression:

    2(13(2)2+8(2)+7)(2)2+2(2)+4=2(13(4)+16+7)4+4+4=2(52+16+7)12=2(75)12=15012=252\frac{2(13(2)^2 + 8(2) + 7)}{(2)^2 + 2(2) + 4} = \frac{2(13(4) + 16 + 7)}{4 + 4 + 4} = \frac{2(52 + 16 + 7)}{12} = \frac{2(75)}{12} = \frac{150}{12} = \frac{25}{2}

Thus, the final value of the limit is:

252\boxed{\frac{25}{2}}


Would you like more details on any step of the process?

Here are five questions to further your understanding:

  1. How do you identify indeterminate forms like 00\frac{0}{0}?
  2. What are some alternative ways to solve limits aside from factoring?
  3. Can L'Hopital's Rule be applied in this problem? If so, how?
  4. Why is factoring an effective method for solving limits involving indeterminate forms?
  5. How can you verify the result of this limit calculation using graphical or numerical methods?

Tip: Always attempt direct substitution first when evaluating limits—it quickly shows if further manipulation is necessary.

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Math Problem Analysis

Mathematical Concepts

Limits
Algebraic Factoring
Indeterminate Forms

Formulas

Direct substitution to check indeterminate form: f(x) = (3x - 1)^3 - (x + 3)^3
Factoring cubic expressions: a^3 - b^3 = (a - b)(a^2 + ab + b^2)

Theorems

Limit Theorems
Factoring Theorem for Polynomials

Suitable Grade Level

Grades 10-12