-- Posted by Just Waiting Here at 12:03 pm on Nov. 26, 2008 Alright, so... I'm pretty sure I got the answer, you can more or less look at it and know it (I hope).  However, I want to know if it's possible to do this problem using calculus. The integral of 2x/(1+x^4). I don't have an integral sign on this thing... so I just need that integrated.  Any substitution that I could make that would work?  And a brief explanation would be great :). -- Posted by Tubbz at 12:15 pm on Nov. 26, 2008 bleurgh! I'm meant to be dong some maths right now. Erm I can't see a substitution you can do. If you find one, let me know. -- Posted by austin s23 at 12:50 pm on Nov. 26, 2008 i wish i could help :/ -- Posted by Just Waiting Here at 3:41 pm on Nov. 26, 2008 Quote: from Tubbz at 12:15 pm on Nov. 26, 2008 bleurgh! I'm meant to be dong some maths right now. Erm I can't see a substitution you can do. If you find one, let me know. It was on a quiz I had, and I would have assumed there would have been a substitution problem in it... I'm pretty sure the answer is arctan (x^2), and that would give you the right answer.... OH.  Duh... That's the substitution!  Haha. u = x^2. Therefore, you have... 2x/(1+u^2)*dx. du = 2xdx. Therefore you have... the integral of 1/(1+u^2)*du 1/(1+u^2) is arctan (u). Then, substituting u=x^2, you get arctan (x^2). Haha, alright, I got it ^__^. -- Posted by Eggo at 9:53 am on Nov. 27, 2008 ^ he got it. Don't forget the +C at the end. XD -- Posted by Just Waiting Here at 10:38 am on Dec. 2, 2008 Quote: from Eggo at 9:53 am on Nov. 27, 2008 ^ he got it. Don't forget the +C at the end. XD Oh... I think I did forget it on the quiz -__-'. I always forget it, unless we're integrating twice, because then I know I ~have~ to have it... Yup... got it back today.  I lost a mark for it.