Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2002
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2002

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Understanding the Output

  • To: mathgroup at smc.vnet.net
  • Subject: [mg32811] Re: [mg32792] Understanding the Output
  • From: BobHanlon at aol.com
  • Date: Thu, 14 Feb 2002 01:43:26 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

In a message dated 2/12/02 7:30:46 AM, smitsky at mindspring.com writes:

>Hi. I'm having trouble understanding some output in Mathematica. If I enter
>Int [x-1] dx, the output I receive is ((-2/3) + (2x/3)) Sqrt(-1+x). If
>I do
>the calculation by hand, I get 2/3.(x-1)^3/2. If I perform:
>FullSimplify(((-2/3) + (2x/3)) Sqrt(-1+x)), I get the same answer
>(2/3.(x-1)^3/2).
>
>With trying to use u-substitution, and figuring more complex Integrals,
>it
>get harder to discern the output. For instance: I tried to evaluate the
>Integral Int [x^3 (1-x^4)^5] dx. I may not be correct, but by hand I got
>1/24.(1-x^4)^6. Mathematica gave a very different output, and using
>FullSimplify didn't seem to help.
>
>Is there any way to get Mathematica to output these values a little
>differently? Am I incorrect on the second example? Any ideas will be
>appreciated. Thanks, Steve
>

Integrate[Sqrt[x-1],x]//Simplify

(2/3)*(x - 1)^(3/2)

Integrate[-x^3 (1-x^4)^5,x]//FullSimplify

(1/24)*x^4*(x^4 - 2)*(x^8 - 3*x^4 + 3)*(x^8 - x^4 + 1)

%-1/24(1-x^4)^6 // Simplify

-(1/24)

They differ by a constant so they are both the integral of the input; 
however, you will not be able to Simplify one to the other since they are not 
equal.


Bob Hanlon
Chantilly, VA  USA


  • Prev by Date: Re: Stumped again on a simple list
  • Next by Date: simulating random variables
  • Previous by thread: Understanding the Output
  • Next by thread: Re: Understanding the Output