Integration

[al78]

Hi all you bright things. Can you help on this one please?

Integrate Ln[x]/(1+x^2) dx

Or suggest a good substitution which splits the integral in such a way that I can show the answer is zero when the limits are zero to Infinity.

Substitutions I get then get stuck with are x=e^u, x=Tan, ....

I can do this easily for Ln[x]/(1+x)^2 dx (it can be done by parts but a nice answer falls out when not done by parts).

I was wondering if you can do this via integration by parts:

Integral(f(x)g'(x))dx = f(x)g(x)-Integral(f'(x)g(x))dx (1)

Let ln(x) = g'(x) (integral of ln(x) is 1/x) and let f(x)=1/(1+x^2) (easy to differentiate)

Sub that into (1) and hopefully you will end up with something that is easier to integrate.

 

[darth vadar]

What sort of things are you interested in?

Winding up so called 'intellectuals' on this message board who have absolutely no sense of humour !!!

 

[marinyork]

Winding up so called 'intellectuals' on this message board who have absolutely no sense of humour !!!

You have it all wrong
View: http://www.youtube.com/watch?v=09XQLmBNrCo

 

[rich p]

Winding up so called 'intellectuals' on this message board who have absolutely no sense of humour !!!

and you have?

 

[dan_bo]

I've been thinking about this and am far from convinced it will work. Could you show your working as to why this works for -ix and ix?

Now, I'm an engineer that's terminally crap at maths and there's the reason. Can someone please explain how you can show your working in a a number that doesn't exist please?

 

[dan_bo]

I've been thinking about this and am far from convinced it will work. Could you show your working as to why this works for -ix and ix?

Now, I'm an engineer that's terminally crap at maths and there's the reason. Can someone please explain how you can show your working in a a number that doesn't exist please?

 

[dan_bo]

I've been thinking about this and am far from convinced it will work. Could you show your working as to why this works for -ix and ix?

Now, I'm an engineer that's terminally crap at maths and there's the reason. Can someone please explain how you can show your working in a a number that doesn't exist please?

 

[dan_bo]

I've been thinking about this and am far from convinced it will work. Could you show your working as to why this works for -ix and ix?

Now, I'm an engineer that's terminally crap at maths and there's the reason. Can someone please explain how you can show your working in a a number that doesn't exist please?

 

[dan_bo]

But just the once will do.

 

[marinyork]

Now, I'm an engineer that's terminally crap at maths and there's the reason. Can someone please explain how you can show your working in a a number that doesn't exist please?

I believe they work on football transfer deadline days, but they tend to get the real and imaginary parts mixed up. It's hard to differentiate between players even though they operate well over a field.

 

[dan_bo]

Cheers kidder. That's monged me up even more.

 

[vernon]

You are actually asleep and dreaming about this thread (which isn't real).

But it's the root cause of my catatonic state.

 

[darth vadar]

and you have?

I don't know whether I have or whether I haven't. But, I find it mildly amusing that anybody can get excited about something so mind numbingly boring.

Perhaps it is a bunch of insecure intellectuals feeling the need to have to continually tell themselves that they are superior by discussing subjects that mere mortals cannot possibly be expected to understand?

Sorry, got to go now as I have some fluff that needs removing from my belly button.

 

[vernon]

I don't know whether I have or whether I haven't. But, I find it mildly amusing that anybody can get excited about something so mind numbingly boring.

Perhaps it is a bunch of insecure intellectuals feeling the need to have to continually tell themselves that they are superior by discussing subjects that mere mortals cannot possibly be expected to understand?

Sorry, got to go now as I have some fluff that needs removing from my belly button.

I'm secure enough and happy enough to acknowledge that some folks' knowledge about some subjects will exclude me from some discussion threads.

There is no compulsion to participate in all threads and I'm not sure that the feeling of insecurity lies with the posters on the more interesting and exotic threads - it could be closer to home.

 

[rich p]

I'm secure enough and happy enough to acknowledge that some folks' knowledge about some subjects will exclude me from some discussion threads.

There is no compulsion to participate in all threads and I'm not sure that the feeling of insecurity lies with the posters on the more interesting and exotic threads - it could be closer to home.

He's got you bang to rights Darth. I'll say no more