Integral of sqrt(1+ln x)/(x*ln x), this is driving me nuts.

In summary, the conversation discusses a question about finding the integral of a function involving the square root of natural logarithms. The individuals suggest different substitution methods and eventually come to the realization that a double substitution is the most efficient approach. One individual also points out a mistake in their previous solution.
  • #1
DrummingAtom
659
2

Homework Statement



Integral of sqrt(1+ln x)/(x*ln x)

Homework Equations





The Attempt at a Solution



I've tried substitutions and they seem to lead to nowhere. I need help getting started on this one. Thanks
 
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  • #2
Oooppss. I got it now, I had to double substitute.
 
  • #3
Did you try u^2=log(x)+1? So log(x)=u^2-1.
 
  • #4
Did you try y = ln x? That should give something that you can probably integrate by using hyperbolic functions.
 
  • #5
DrummingAtom said:
Oooppss. I got it now, I had to double substitute.

But...why?

u=lnx, du=1/x

thus sqrt(u)du/u= u^(-1/2)du...easy power rule, and that's only one sub...

==============
Edit: Thank you DrummingAtom for showing me an error, the likes I have made many a time.
 
Last edited:
  • #6
Apphysicist said:
But...why?

u=lnx, du=1/x

thus sqrt(u)du/u= u^(-1/2)du...easy power rule, and that's only one sub...

But where does the 1 go? The answer would then be 2sqrt(ln x) which doesn't equal the original function.
 
  • #7
DrummingAtom said:
But where does the 1 go? The answer would then be 2sqrt(ln x) which doesn't equal the original function.

Well you see, that would just be me neglecting the one to make it an easy question. xD

My bad.
 
  • #8
=) no worries. This problem gave me about 1.5 hours of sloppy algebra and confusion. I love Sunday nights.
 

Related to Integral of sqrt(1+ln x)/(x*ln x), this is driving me nuts.

1. What is the definition of an integral?

An integral is a mathematical concept that represents the accumulation or total value of a quantity, typically represented as the area under a curve in a graph. It is used to find the exact or approximate value of a function over a given interval.

2. How do you solve an integral?

To solve an integral, you can use various methods such as substitution, integration by parts, or trigonometric substitution. In this case, the integral of sqrt(1+ln x)/(x*ln x) can be solved using integration by parts.

3. What is the purpose of finding an integral?

The main purpose of finding an integral is to solve problems involving the accumulation of a quantity over a given interval. It is also used in various fields such as physics, engineering, and economics to calculate important values and make predictions.

4. How do you know when to use a specific integration technique?

The choice of integration technique depends on the form of the integrand. Generally, it is helpful to try different techniques and see which one works best. In this case, integration by parts is a suitable method as the integrand contains a product of two functions.

5. Is there a shortcut or trick to solving integrals?

There are certain integrals that have well-known solutions and can be solved using shortcuts such as integration tables or computer programs. However, most integrals require a combination of techniques and may not have a straightforward solution. Therefore, it is important to have a good understanding of different integration techniques and when to use them.

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