The Student Room Group

Stuck on easy integration question - HELP!!

Integral of arctan(3x)/[x(1+x^2)] between x=0 and x=infinity.
Original post by Ano123
Integral of arctan(3x)/[x(1+x^2)] between x=0 and x=infinity.

...

Edit: Have you written down the question correctly? Wolfram Alpha doesn't give a nice answer :lolwut:.

Edit: I input it wrong. It's solvable.
(edited 8 years ago)
Reply 2
easy??
Reply 3
Started working this out, and you're going to get a horrific equation at the end - are you sure it's asin?
Reply 4
πln2 :u:
Reply 5
Definitely arctan
Reply 6
Original post by B_9710
πln2 :u:


How?
Reply 7
Original post by Kurwaaaa
How?

How what?
Original post by B_9710
How what?


DId you get the answer, I presume :tongue:.
Reply 9
Original post by Kurwaaaa
How?


kurwa how
Reply 10
Original post by Kvothe the arcane
DId you get the answer, I presume :tongue:.


Differentiation under the integral sign. :wink:
Original post by B_9710
Differentiation under the integral sign. :wink:


Ah, one of those techniques. Thank you :smile:. Any chance you can help the OP?
Reply 12
Original post by TeeEm
easy??


Compared to hard integral thread?
Reply 13
Original post by B_9710
Compared to hard integral thread?


definitely not A level
Hmmm...I have (x*arctan(3x)-1/6(ln(1+9x^2)))*ln(x)*arctan(x)
Where did I go wrong? And how do I do the limits?
(edited 8 years ago)
Reply 15
Original post by Username002
Hmmm...I have (x*arctan(3x)-1/6(ln(1+9x^2)))*ln(x)*arctan(x)
Where did I go wrong? And how do I do the limits?


What integration technique have you used?
I split the integral up. Can I even do that? I split it up into three integrals.
arctan(3x), 1/x and 1/(1+x^2)
(edited 8 years ago)
Reply 17
Original post by Username002
I split the integral up. Can I even do that? I split it up into three integrals.
arctan(3x), 1/x and 1/(1+x^2)


You cannot do that, the integrand is a product of those 3 terms so you cannot split it up in this way.
If I may ask what level of maths are you currently working at?
(edited 8 years ago)
A level, why?

Quick Reply

Latest