Some weird integral with natural logarithm

In summary, the problem is to find the integral of the function (\ln x / x)^2. The student attempted to solve it by using the substitution u = \ln^2 x and dv = the rest, or dv = \ln^2 x dx and u = the rest, but both attempts were unsuccessful. Another approach was suggested, using u = \ln x and du = 1/x dx. This would simplify the integrand to [(u^2) / x] du. Finally, the correct dv was determined to be dv = 1/x^2 dx, leading to the final form of the integral as (u^2)exp(-u) du.
  • #1
mrdoe
36
0

Homework Statement



[tex]\displaystyle\int\left(\dfrac{\ln x}{x}\right)^2 dx[/tex]

2. The attempt at a solution

I tried letting [tex]u=\ln^2 x[/tex] and dv the rest and I also tried [tex]dv=\ln^2 x dx[/tex] and u the rest. It won't work out.
 
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  • #2
Let u = ln(x), => du = 1/x dx.

Then your integrand is [(u^2) / x]du

Well, x = exp(u), so what you really have is (u^2)exp(-u)du

Does that work? You should be able to handle that one...
 
  • #3
mrdoe said:

Homework Statement



[tex]\displaystyle\int\left(\dfrac{\ln x}{x}\right)^2 dx[/tex]

2. The attempt at a solution

I tried letting [tex]u=\ln^2 x[/tex] and dv the rest and I also tried [tex]dv=\ln^2 x dx[/tex] and u the rest. It won't work out.

your dv is wrong its [tex]dv=\frac{1}{x^2} dx[/tex]
 

1. What is the natural logarithm?

The natural logarithm, denoted as ln(x) or loge(x), is a mathematical function that gives the power to which the base number e (approximately 2.71828) must be raised to equal a given number x. It is the inverse function of the exponential function.

2. What does the integral with natural logarithm represent?

The integral with natural logarithm represents the area under the curve of a function that includes the natural logarithm. It is a mathematical operation used to find the antiderivative of a function, which can be used to solve various problems in mathematics and science.

3. How do you solve a weird integral with natural logarithm?

Solving a weird integral with natural logarithm requires using integration techniques such as substitution, integration by parts, or partial fractions. It is important to follow the correct steps and apply the appropriate technique to evaluate the integral.

4. What are some real-world applications of integrals with natural logarithms?

Integrals with natural logarithms have many applications in fields such as physics, chemistry, economics, and engineering. They are used to model growth and decay, calculate work and energy, and solve optimization problems, among other things.

5. Can you provide an example of a weird integral with natural logarithm?

One example of a weird integral with natural logarithm is ∫ ln(x)/x dx. This integral can be solved using integration by parts, where u = ln(x) and dv = dx/x. The resulting integral can then be evaluated using the logarithmic and inverse tangent functions.

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