Math Problem Statement

Evaluate the limit: \[ \lim_{n \to \infty} \left( \sqrt[3]{n} \cdot \left( \sqrt[3]{n^2} - 3\sqrt[3]{n(n-1)} \right) \right) \]

Solution

The problem is to evaluate the limit:

[ \lim_{n \to \infty} \left( \sqrt[3]{n} \cdot \left( \sqrt[3]{n^2} - 3\sqrt[3]{n(n-1)} \right) \right) ]

First, notice that n23=n2/3\sqrt[3]{n^2} = n^{2/3} and n(n1)3\sqrt[3]{n(n-1)} can be approximated as n2n3=(n2n)1/3\sqrt[3]{n^2 - n} = (n^2 - n)^{1/3}. As nn becomes very large, the term n-n inside the cube root becomes insignificant compared to n2n^2, so n(n1)3n2/3\sqrt[3]{n(n-1)} \approx n^{2/3}. Therefore, we can simplify the expression:

[ \sqrt[3]{n^2} - 3\sqrt[3]{n(n-1)} \approx n^{2/3} - 3n^{2/3} = -2n^{2/3} ]

Now, substituting this back into the original limit:

limn(n3(2n2/3))=limn2n3/3=limn2n=\lim_{n \to \infty} \left( \sqrt[3]{n} \cdot (-2n^{2/3}) \right) = \lim_{n \to \infty} -2n^{3/3} = \lim_{n \to \infty} -2n = -\infty

Thus, the limit diverges to -\infty.

Would you like further details on this problem or any related concept? Here are some additional questions you could consider:

  1. What happens if we do not approximate and calculate n(n1)3\sqrt[3]{n(n-1)} exactly?
  2. How would the limit change if the constant 33 in the expression was a different constant?
  3. Can this method be used for limits involving other functions with nkn^{k} where kk is not 2/32/3?
  4. What are other techniques to evaluate limits involving cube roots?
  5. How does the behavior of n(n1)3\sqrt[3]{n(n-1)} compare to n23\sqrt[3]{n^2} as nn approaches infinity?

Tip: When evaluating limits of sequences involving roots, consider the leading terms as nn grows, as they will have the most significant impact on the limit's value.

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Math Problem Analysis

Mathematical Concepts

Limits
Cube Roots
Asymptotic Analysis

Formulas

Cube root formula: \(\sqrt[3]{x} = x^{1/3}\)
Approximation: \(n(n-1)^{1/3} \approx n^{2/3}\)

Theorems

Limit Theorem
Asymptotic behavior of cube roots

Suitable Grade Level

Undergraduate Calculus