Math Problem Statement

Вычислить несобственный интеграл \(\int_{-3}^{2} \frac{dx}{(x + 3)^2}\) или доказать его расходимость (сходимость).

Solution

The problem asks us to evaluate the improper integral:

32dx(x+3)2\int_{-3}^{2} \frac{dx}{(x + 3)^2}

or prove its divergence (or convergence). Let us solve it step by step.


Step 1: Analyze the function and detect possible singularities

The function to integrate is:

f(x)=1(x+3)2.f(x) = \frac{1}{(x + 3)^2}.

  • The denominator (x+3)2(x + 3)^2 becomes zero at x=3x = -3, which means x=3x = -3 is a singular point.
  • Thus, the integral is improper due to the singularity at x=3x = -3. We will need to analyze it as a limit to check for convergence or divergence.

Step 2: Rewrite the integral as a limit

The improper integral is rewritten as:

32dx(x+3)2=limε0+(3+ε2dx(x+3)2).\int_{-3}^{2} \frac{dx}{(x + 3)^2} = \lim_{\varepsilon \to 0^+} \left( \int_{-3 + \varepsilon}^{2} \frac{dx}{(x + 3)^2} \right).


Step 3: Evaluate the antiderivative of 1(x+3)2\frac{1}{(x + 3)^2}

We calculate the indefinite integral of 1(x+3)2\frac{1}{(x + 3)^2}:

1(x+3)2dx=1x+3+C.\int \frac{1}{(x + 3)^2} dx = -\frac{1}{x + 3} + C.


Step 4: Substitute the limits

Using the antiderivative, the integral becomes:

3+ε2dx(x+3)2=[1x+3]3+ε2.\int_{-3 + \varepsilon}^{2} \frac{dx}{(x + 3)^2} = \left[ -\frac{1}{x + 3} \right]_{-3 + \varepsilon}^{2}.

Substitute the bounds: [1x+3]3+ε2=12+3(1(3+ε)+3).\left[ -\frac{1}{x + 3} \right]_{-3 + \varepsilon}^{2} = -\frac{1}{2 + 3} - \left(-\frac{1}{(-3 + \varepsilon) + 3}\right).

Simplify: =15(1ε).= -\frac{1}{5} - \left(-\frac{1}{\varepsilon}\right). =15+1ε.= -\frac{1}{5} + \frac{1}{\varepsilon}.


Step 5: Analyze the limit as ε0+\varepsilon \to 0^+

As ε0+\varepsilon \to 0^+, the term 1ε\frac{1}{\varepsilon} tends to infinity. Thus, the integral diverges because the singularity at x=3x = -3 causes the value to blow up.


Conclusion

The improper integral 32dx(x+3)2\int_{-3}^{2} \frac{dx}{(x + 3)^2} diverges.


Would you like further clarification or details on any step? Let me know!
Here are 5 related questions to expand your understanding:

  1. What are the different types of improper integrals, and how do we analyze their convergence?
  2. How would the solution change if the power in the denominator were (x+3)p(x + 3)^p, where p>2p > 2?
  3. What are common techniques to evaluate improper integrals with infinite limits?
  4. Can you explain why 1ε\frac{1}{\varepsilon} causes divergence as ε0+\varepsilon \to 0^+?
  5. How can improper integrals be applied to real-world problems, such as physics or probability?

Tip: When analyzing improper integrals, always check for singularities or infinite bounds before attempting to evaluate them.

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Math Problem Analysis

Mathematical Concepts

Improper integrals
Limits
Antiderivatives
Divergence

Formulas

Indefinite integral formula: \(\int \frac{1}{(x + c)^2} dx = -\frac{1}{x + c} + C\)
Limit evaluation of improper integrals: \(\int_{a}^{b} f(x) dx = \lim_{\varepsilon \to 0^+} \int_{a+\varepsilon}^{b} f(x) dx\)

Theorems

Convergence and divergence of improper integrals

Suitable Grade Level

Undergraduate Mathematics