/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 65 In Exercises 65 and \(66,\) use ... [FREE SOLUTION] | 91Ó°ÊÓ

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In Exercises 65 and \(66,\) use a CAS to perform the integrations. Evaluate the integrals $$ (a)\int x \ln x d x \quad \text { b. } \int x^{2} \ln x d x \quad \text { c. } \int x^{3} \ln x d x $$ $$ \begin{array}{l}{\text { d. What pattern do you see? Predict the formula for } \int x^{4} \ln x d x} \\ {\text { and then see if you are correct by evaluating it with a CAS. }} \\ {\text { e. What is the formula for } \int x^{n} \ln x d x, n \geq 1 ? \text { Check your }} \\ {\text { answer using a CAS. }}\end{array} $$

Short Answer

Expert verified
\( \int x^n \ln x \, dx = \frac{x^{n+1}}{n+1} \ln x - \frac{x^{n+1}}{(n+1)^2} + C \) for \( n \geq 1 \).

Step by step solution

01

Understanding the problem

We need to evaluate four separate integrals involving the natural logarithm and a power of x. Additionally, we need to identify a pattern through these integrations and predict a general formula for any power of x.
02

Solve Part (a)

To integrate \( \int x \ln x \, dx \), use integration by parts. Let \( u = \ln x \) and \( dv = x \, dx \). Then \( du = \frac{1}{x} \, dx \) and \( v = \frac{x^2}{2} \). Thus, \( \int x \ln x \, dx = \frac{x^2}{2} \ln x - \int \frac{x^2}{2} \cdot \frac{1}{x} \, dx = \frac{x^2}{2} \ln x - \frac{x^2}{4} + C \).
03

Solve Part (b)

Use the integration by parts method again for \( \int x^2 \ln x \, dx \). Set \( u = \ln x \) and \( dv = x^2 \, dx \), which gives \( du = \frac{1}{x} \, dx \) and \( v = \frac{x^3}{3} \). The integral becomes \( \frac{x^3}{3} \ln x - \int \frac{x^3}{3} \, \frac{1}{x} \, dx = \frac{x^3}{3} \ln x - \frac{x^3}{9} + C \).
04

Solve Part (c)

Apply integration by parts for \( \int x^3 \ln x \, dx \) in similar fashion: let \( u = \ln x \) and \( dv = x^3 \, dx \), so \( du = \frac{1}{x} \, dx \) and \( v = \frac{x^4}{4} \). Thus, \( \frac{x^4}{4} \ln x - \int \frac{x^4}{4} \, \frac{1}{x} \, dx = \frac{x^4}{4} \ln x - \frac{x^4}{16} + C \).
05

Identify the pattern

Based on the results from steps 2 to 4, notice that each integral of the form \( \int x^n \ln x \, dx \) results in a function of the form \( \frac{x^{n+1}}{n+1} \ln x - \frac{x^{n+1}}{(n+1)^2} \).
06

Predict and verify Part (d)

Predict that \( \int x^4 \ln x \, dx = \frac{x^5}{5} \ln x - \frac{x^5}{25} + C \). Use a CAS to verify the calculated integral, and confirm that it matches the pattern established.
07

Generalize and evaluate Part (e)

The formula for \( \int x^n \ln x \, dx \) is predicted to be \( \frac{x^{n+1}}{n+1} \ln x - \frac{x^{n+1}}{(n+1)^2} + C \) for any \( n \geq 1 \). Check this general formula using a CAS to ensure its correctness.

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Key Concepts

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

Definite Integrals
Definite integrals are a core concept in calculus. They are used to find the area under a curve, between two points, on the x-axis. Mathematically, a definite integral from a to b of a function f(x) is written as \( \int_{a}^{b} f(x) \, dx \). The resulting value gives the total accumulation of quantities such as area, displacement, or resources. A definite integral has limits of integration, which define the interval over which integration occurs.
The process involves calculating the antiderivative of the given function, evaluating it at the upper and lower limit, and subtracting the results. Calculus provides the fundamental theorem of calculus to seamlessly connect differentiation and integration, allowing computations to switch between these concepts with precision and efficiency.
Natural Logarithm
The natural logarithm, denoted as \( \ln x \), is a logarithm with base \( e \), where \( e \) is approximately 2.71828. It is fundamental in calculus due to its unique properties which simplify the differentiation and integration of exponential functions. One key feature is that the derivative of \( \ln x \) is \( \frac{1}{x} \).
Its inversion property: if \( y = \ln x \), then \( x = e^y \), makes it highly useful in solving equations involving exponential functions. The natural logarithm is applicable in scenarios where there's a continuous compound growth or decay, making it vital in diverse fields such as economics, biology, and physics.
Calculus Patterns
In calculus, recognizing patterns through various functions and operations helps simplify complex problems. A prominent pattern observed in integration problems, like the ones given, is how the coefficients change systematically. Calculus patterns often involve sequences and symmetries that allow prediction of results for higher or varied terms.
For the exercise at hand, a known pattern was derived from repeatedly applying integration by parts. Each integration follows a consistent progression, yielding a predictable result structure which can then be generalized for any polynomial power of x. These recognizable patterns offer a strategic pathway to tackle similar integrals effortlessly. Understanding these allows students to anticipate results without solving every single integral from first principles.
Symbolic Computation
Symbolic computation is the process of solving mathematical problems symbolically rather than numerically, allowing for exact representation of calculations. This is vital in calculus for deriving general formulas and verifying results quickly and efficiently. Computations are handled by tools like Computer Algebra Systems (CAS), which manage complex algebraic manipulations.
In the integration exercises, symbolic computation aids in predicting general formulas without computing every intermediate step manually. These systems verify pattern predictions by confirming the solutions' validity, ensuring that the mathematical operations conform to expected outcomes. This technology not only optimizes solving processes but allows students and professionals alike to focus on understanding underlying principles rather than getting bogged down in tedious calculations.

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Most popular questions from this chapter

In Exercises \(27-40\) , use a substitution to change the integral into one you can find in the table. Then evaluate the integral. $$ \int \frac{d y}{y \sqrt{3+(\ln y)^{2}}} $$

Usable values of the sine-integral function The sine-integral function, $$\operatorname{Si}(x)=\int_{0}^{x} \frac{\sin t}{t} d t$$ is one of the many functions in engineering whose formulas cannot be simplified. There is no elementary formula for the antiderivative of \((\sin t) / t .\) The values of \(S \mathrm{Si}(x),\) however, are readily estimated by numerical integration. Although the notation does not show it explicitly, the function being integrated is $$f(t)=\left\\{\begin{array}{cl}{\frac{\sin t}{t},} & {t \neq 0} \\ {1,} & {t=0}\end{array}\right.$$ the continuous extension of \((\sin t) / t\) to the interval \([0, x]\) . The function has derivatives of all orders at every point of its domain. Its graph is smooth, and you can expect good results from Simpson's Rule. a. Use the fact that \(\left|f^{(4)}\right| \leq 1\) on \([0, \pi / 2]\) to give an upper bound for the error that will occur if $$\mathrm{Si}\left(\frac{\pi}{2}\right)=\int_{0}^{\pi / 2} \frac{\sin t}{t} d t$$ is estimated by Simpson's Rule with \(n=4\) b. Estimate \(\operatorname{Si}(\pi / 2)\) by Simpson's Rule with \(n=4\) . c. Express the error bound you found in part (a) as a percentage of the value you found in part (b).

In Exercises \(87-90,\) use a CAS to explore the integrals for various values of \(p\) (include noninteger values). For what values of \(p\) does the integral converge? What is the value of the integral when it does converge? Plot the integrand for various values of \(p\) . $$\int_{0}^{e} x^{p} \ln x d x$$

Effects of an antihistamine The concentration of an antihistamine in the bloodstream of a healthy adult is modeled by $$C=12.5-4 \ln \left(t^{2}-3 t+4\right)$$ where \(C\) is measured in grams per liter and \(t\) is the time in hours since the medication was taken. What is the average level of concentration in the bloodstream over a 6 -hr period?

Use reduction formulas to evaluate the integrals in Exercises \(41-50 .\) $$ \int 2 \sec ^{3} \pi x d x $$

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