Math Problem Statement

Solve the limits provided in the uploaded image.

Solution

Here are the problems from the image (translated as needed) with corresponding solutions:


1. limnn3+2n13n+1\lim_{n \to \infty} \frac{\sqrt[3]{n^3 + 2n - 1}}{n + 1}

Solution:

Factor nn from the terms inside the cube root and the denominator: n3(1+2n21n3)3n(1+1n)\frac{\sqrt[3]{n^3(1 + \frac{2}{n^2} - \frac{1}{n^3})}}{n(1 + \frac{1}{n})} =n1+2n21n33n(1+1n).= \frac{n \cdot \sqrt[3]{1 + \frac{2}{n^2} - \frac{1}{n^3}}}{n(1 + \frac{1}{n})}. As nn \to \infty, 1+2n21n331\sqrt[3]{1 + \frac{2}{n^2} - \frac{1}{n^3}} \to 1 and (1+1n)1(1 + \frac{1}{n}) \to 1: limn=11=1.\lim_{n \to \infty} = \frac{1}{1} = 1.


2. limx1x23x+2x36x2+11x6\lim_{x \to 1} \frac{x^2 - 3x + 2}{x^3 - 6x^2 + 11x - 6}

Solution:

Factor both numerator and denominator: (x1)(x2)(x1)(x2)(x3).\frac{(x - 1)(x - 2)}{(x - 1)(x - 2)(x - 3)}. Cancel (x1)(x2)(x - 1)(x - 2), leaving: 1x3.\frac{1}{x - 3}. At x=1x = 1, x3=2x - 3 = -2, so: limx1=12.\lim_{x \to 1} = -\frac{1}{2}.


3. limx01cos4x6x2\lim_{x \to 0} \frac{1 - \cos 4x}{6x^2}

Solution:

Using the small-angle approximation cos4x1(4x)22\cos 4x \approx 1 - \frac{(4x)^2}{2}, we have: 1cos4x6x216x226x2=86=43.\frac{1 - \cos 4x}{6x^2} \approx \frac{\frac{16x^2}{2}}{6x^2} = \frac{8}{6} = \frac{4}{3}.


4. limx0e2x13x\lim_{x \to 0} \frac{e^{2x} - 1}{3x}

Solution:

Using the Taylor expansion e2x1+2xe^{2x} \approx 1 + 2x, we get: e2x13x2x3x=23.\frac{e^{2x} - 1}{3x} \approx \frac{2x}{3x} = \frac{2}{3}.


5. limx2(x+1x2)2x+1\lim_{x \to 2} \left( \frac{x + 1}{x - 2} \right)^{2x + 1}

Solution:

Let y=(x+1x2)2x+1y = \left( \frac{x + 1}{x - 2} \right)^{2x + 1} and take the logarithm: lny=(2x+1)ln(x+1x2).\ln y = (2x + 1) \ln \left( \frac{x + 1}{x - 2} \right). As x2x \to 2, 2x+152x + 1 \to 5 and ln(x+1x2)\ln \left( \frac{x + 1}{x - 2} \right) \to \infty. The limit diverges to \infty.


6. limx01+x31x2\lim_{x \to 0} \frac{\sqrt[3]{1 + x} - 1}{x^2}

Solution:

Expand 1+x3\sqrt[3]{1 + x} using the binomial theorem: 1+x31+x3.\sqrt[3]{1 + x} \approx 1 + \frac{x}{3}. The numerator becomes: 1+x31x3.\sqrt[3]{1 + x} - 1 \approx \frac{x}{3}. Thus: 1+x31x2x3x2=13x.\frac{\sqrt[3]{1 + x} - 1}{x^2} \approx \frac{\frac{x}{3}}{x^2} = \frac{1}{3x}. As x0x \to 0, the limit diverges to \infty.


7. limn1+3+5++(2n1)n+12n+12\lim_{n \to \infty} \frac{1 + 3 + 5 + \dots + (2n - 1)}{n + 1} \cdot \frac{2n + 1}{2}

Solution:

The sum of the first nn odd numbers is: 1+3+5++(2n1)=n2.1 + 3 + 5 + \dots + (2n - 1) = n^2. Substitute this into the expression: n2n+12n+12.\frac{n^2}{n + 1} \cdot \frac{2n + 1}{2}. Factor out n2n^2 in the numerator and simplify: n2n+12n+12n2nn=n2.\frac{n^2}{n + 1} \cdot \frac{2n + 1}{2} \approx \frac{n^2}{n} \cdot n = \frac{n}{2}. As nn \to \infty, the limit grows without bound (\infty).


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Relative Questions:

  1. What is the significance of L'Hôpital's Rule in solving indeterminate limits?
  2. How does Taylor series approximation simplify solving limits involving exponential or trigonometric functions?
  3. Why does the binomial theorem help when expanding fractional powers near zero?
  4. Can the logarithmic transformation simplify more complex limit problems involving exponents?
  5. How does divergence behave differently for polynomial versus transcendental growth rates?

Tip: When dealing with \infty or 0/00/0 limits, always check if L'Hôpital's Rule or series expansions simplify the problem before direct substitution.

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Math Problem Analysis

Mathematical Concepts

Limits
Algebraic Simplification
Taylor Series Expansion
Binomial Theorem
Indeterminate Forms
Asymptotic Behavior

Formulas

L'Hôpital's Rule: lim(x->a) f(x)/g(x) = f'(x)/g'(x) if lim(x->a) f(x)/g(x) = 0/0 or ±∞/±∞
Taylor Expansion: e^x ≈ 1 + x for small x
Binomial Approximation: (1 + x)^n ≈ 1 + nx for small x and |n| < ∞

Theorems

Squeeze Theorem
Properties of Exponents
Factorization Techniques for Polynomials

Suitable Grade Level

Undergraduate (Calculus I and II)