Math Problem Statement

Compute the limit of the function: lim (h -> 0) [(cube root of (27 + h)) - 3] / h.

Solution

The given problem requires finding the limit:

limh027+h33h.\lim_{h \to 0} \frac{\sqrt[3]{27 + h} - 3}{h}.

Solution:

Step 1: Recognize the indeterminate form

As h0h \to 0, the numerator becomes 2733=33=0\sqrt[3]{27} - 3 = 3 - 3 = 0 and the denominator is also h=0h = 0. Therefore, this is an indeterminate form of the type 00\frac{0}{0}, and we need to resolve it.

Step 2: Use the expansion of a cube root

The cube root function x3\sqrt[3]{x} can be expanded as: [ \sqrt[3]{27 + h} = \sqrt[3]{27} + \frac{1}{3 \cdot \sqrt[3]{27^2}} h + \mathcal{O}(h^2), ] where 273=3\sqrt[3]{27} = 3.

Step 3: Substitute the expansion into the limit

Substitute 27+h3=3+h27+O(h2)\sqrt[3]{27 + h} = 3 + \frac{h}{27} + \mathcal{O}(h^2) into the numerator: 27+h33h=(3+h27+O(h2))3h.\frac{\sqrt[3]{27 + h} - 3}{h} = \frac{\left(3 + \frac{h}{27} + \mathcal{O}(h^2)\right) - 3}{h}.

Simplify: 27+h33h=h27+O(h2)h.\frac{\sqrt[3]{27 + h} - 3}{h} = \frac{\frac{h}{27} + \mathcal{O}(h^2)}{h}.

Step 4: Simplify further

Divide through by hh: 27+h33h=127+O(h).\frac{\sqrt[3]{27 + h} - 3}{h} = \frac{1}{27} + \mathcal{O}(h).

Step 5: Take the limit as h0h \to 0

As h0h \to 0, the higher-order term O(h)\mathcal{O}(h) vanishes. Thus: limh027+h33h=127.\lim_{h \to 0} \frac{\sqrt[3]{27 + h} - 3}{h} = \frac{1}{27}.

Final Answer:

127\boxed{\frac{1}{27}}

Let me know if you want further clarification or details about this problem! Here are five questions to deepen understanding:

  1. What other methods could you use to evaluate this limit (e.g., L'Hopital's Rule)?
  2. How does the expansion for x3\sqrt[3]{x} help in simplifying the limit?
  3. Can you generalize this technique for other roots, such as square roots?
  4. What would happen if hh were not approaching 00?
  5. Why is the higher-order term O(h2)\mathcal{O}(h^2) negligible in this limit?

Tip: For indeterminate forms like 00\frac{0}{0}, using expansions or derivatives often simplifies the evaluation.

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Math Problem Analysis

Mathematical Concepts

Limits
Indeterminate Forms
Expansion of Cube Roots

Formulas

Expansion of cube root: cube_root(a + b) = cube_root(a) + (b / [3 * a^(2/3)]) + higher-order terms
Simplification of indeterminate forms using series expansions

Theorems

Limit definition for indeterminate forms
Expansion for cube roots

Suitable Grade Level

Grade 11-12 or Early College