Quoting Post Archived Topic: It will not be bumped to the top of the forum. Topic Substitution? Math Question Membername   Not a member? Sign Up Free (takes 20 seconds) Password   Forgotten your password? Post Font: Verdana Arial Black Georgia Comic Sans Impact   Size: Tiny Normal Big Huge   Color: Default Dark Red Red Orange Brown Green Olive Cyan Blue Dark Blue Indigo Black [ Check Spelling ] [ Post Preview ] [ LiveTags ] Quote: from [m]Just Waiting Here[/m] at 3:41 pm on Nov. 26, 2008[quote]Quote: from [m]Tubbz[/m] at 12:15 pm on Nov. 26, 2008[quote]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.[/quote] 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 ^__^.[/quote] FAQ Keyword Search: Post Options Favorites Manager Notify me of new replies to this topic by email Notify me of new replies to this topic by private message Original Post Just Waiting Here Posted 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 :).

Replies Just Waiting Here Posted 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. Eggo Posted at 9:53 am on Nov. 27, 2008 ^ he got it. Don't forget the +C at the end. XD Just Waiting Here Posted 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 ^__^. austin s23 Posted at 12:50 pm on Nov. 26, 2008 i wish i could help :/ Tubbz Posted 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. All 5 previous replies displayed.