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In Exercises \(7-51\), find or evaluate the integral. $$ \int \frac{2 r^{2}-3 r+4}{\left(r^{2}+2\right)^{2}} d r $$

Short Answer

Expert verified
The short version of the answer is: \[ \int \frac{2 r^{2}-3 r+4}{\left(r^{2}+2\right)^{2}} d r = -\frac{(2r^2 - 3r + 4)}{2(r^2 + 2)} +\frac{(r - \frac34)^3}{3} - \frac{15r}{8} + C \]

Step by step solution

01

Simplify the expression if possible

We need to check if there is any suitable substitution that can simplify the expression. In this case, we can try using substitution u = r^2 + 2 $$ u = r^2 + 2 \\ \frac{du}{dr} = 2r $$ If we simplify the given expression with this substitution, we get: $$ \int \frac{(2r^2 - 3r + 4) (dr/du)}{(r^2 + 2)^2} du $$ We see that this substitution will not simplify the expression. So, let's go to the next step and try integration by partial fractions.
02

Decomposition of the function by partial fractions

Since we are unable to simplify the expression by substitution, let's try to decompose it using partial fractions method. However, since the denominator is \((r^2 + 2)^2\), but the numerator degree is less than the denominator, incomplete integration by parts can be efficient.
03

Integration by parts

Let's now apply integration by parts rule, with: $$ u = 2r^2 - 3r + 4, \ dv = \frac{dr}{(r^2 + 2)^2} $$ Now, we find du and v: $$ du = (4r - 3) dr,\quad v = -\frac{1}{2(r^2 + 2)} $$ Now, using the integration by parts formula: $$ \int udv = uv - \int vdu = \left[-\frac{(2r^2 - 3r + 4)}{2(r^2 + 2)}\right] + \frac12\int \frac{4r - 3}{r^2 + 2} dr $$
04

Integrate the remaining integral

The remaining integral is $$ \frac12\int \frac{4r - 3}{r^2 + 2} dr $$ We have to find \(A\) and \(B\) so that $$ 4r - 3 = A(r + B) $$ Equating coefficients, we have $$ A = 4,\quad B = -\frac{3}{4}. $$ Now, we can substitute back and find the remaining integral: $$ \frac12\int \frac{4(4r - 3)}{4r^2 + 8} dr = 2\int (r - \frac34)^2 - \frac{15}{16} dr $$ Integrating this, we get: $$ \int (r - \frac34)^2 dr - 2\int \frac{15}{16} dr = \frac{(r - \frac34)^3}{3} - \frac{15r}{8} + C $$
05

Add all parts

Now, combining all parts, we get the final result: $$ \int \frac{2 r^{2}-3 r+4}{\left(r^{2}+2\right)^{2}} d r = -\frac{(2r^2 - 3r + 4)}{2(r^2 + 2)} +\frac{(r - \frac34)^3}{3} - \frac{15r}{8} + C $$

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Substitution Method
The Substitution Method is one of the most straightforward integration techniques. It involves transforming the given integral into a simpler form by substituting parts of the integral with new variables. This typically makes the integral easier to solve.

Essentially, you're replacing a complicated expression with a simpler single variable. In our problem, you might think of setting the substitution as something like \( u = r^2 + 2 \).

However, when you attempt to substitute, make sure that every part of the original integral can be rewritten in terms of this new variable. If not, the substitution may not simplify the way you hope.
  • Choose a substitution that simplifies the variable part of the expression.
  • Differential conversion: Compute \( \frac{du}{dr} \) to adjust the integration measure accordingly.
  • If substitution does not simplify the integral effectively, consider another method.
Even if substitution isn’t successful, understanding how to adjust expressions for substitution gives deeper insight into solving more complex integrals.
Partial Fractions
Partial Fractions is a technique often used with rational expressions, helping to break down a complex fraction into simpler fractions. It’s usually applicable when dealing with polynomial numerators and denominators.

When considering Partial Fractions, check if the degree (highest power) of the numerator is less than that of the denominator. This is crucial as it indicates if the method is appropriate.
  • The basic form of Partial Fractions starts by expressing the integrand as a sum of simpler fractions.
  • You then solve for the coefficients of these simpler fractions.
  • Finally, each fraction is integrated separately.
In our exercise, the degree conditions weren’t perfectly met, which led us toward exploring other integration methods. However, understanding the decomposition step is vital for recognizing potential success even when another method ends up more direct or efficient.
Integration by Parts
Integration by Parts is another cornerstone of Integral Calculus. It hinges on the idea that some intricate integrals can be transformed into simpler parts. Derived from the product rule for differentiation, it is expressed by the formula:
\[\int u \, dv = uv - \int v \, du\]
In this formula, you select expressions within the integral for \( u \) and \( dv \) components. This method is particularly handy when dealing with products of functions.

For our particular problem, we chose \( u = 2r^2 - 3r + 4 \) and \( dv = \frac{dr}{(r^2 + 2)^2} \). This decided pairing enabled computation of \( du \) and \( v \), thereafter allowing the transformation of the original integral into components that were more amenable to individual solution.
  • Select \( u \) and \( dv \) where \( dv \) is easily integrated.
  • Ensure differentiating \( u \) makes the problem simpler.
  • Apply the formula and solve step by step.
This method showcases how shifting perspectives in calculus can make seemingly complex integrals more approachable.
Integral Calculus
Integral Calculus is a major calculus branch focusing on integrals, which are central for computing areas under curves and solving differential equations. It operates through two main options: finding antiderivatives or computing definite integrals.

Working through different techniques of integration is crucial to mastering Integral Calculus. Methods like the Substitution Method, Partial Fractions, and Integration by Parts form the toolkit for tackling various integrals.
  • Integral Calculus bridges functions and graphs, providing ways to measure and accumulate quantities.
  • It includes applications beyond evaluating integrals, like solving area and volume problems.
  • Mastery relies on understanding different integration techniques and knowing when to apply each to solve diverse integral problems.
The core of Integral Calculus lies in visualizing problems, employing methodical approaches, and relying on adeptness at thinking outside the box to find solutions.

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