HP Forum Archive 14

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Trouble integrating on 49g+ Message #1 Posted by JaSon on 7 Feb 2005, 12:13 p.m. If I try to integrate the expression c/(x^n) the calc is unable to integrate it. If I change the n to a number it has no trouble integrating. I have tried changing the flag 105 for exact mode and that doesn't help. Any ideas on what I can do to make the calc integrate with a variable there instead of a number?

Re: Trouble integrating on 49g+ Message #2 Posted by Eddie Shore on 7 Feb 2005, 3:15 p.m., in response to message #1 by JaSon Interesting, I get the same result using c/(x^n) and c*x^-n: both giving c * integral(1/(e^(n*ln x) dx) where the answer should be c*-n*x^(-n-1)

Re: Trouble integrating on 49g+ Message #3 Posted by Vieira, Luiz C. (Brazil) on 7 Feb 2005, 7:34 p.m., in response to message #2 by Eddie Shore Hi Jason, Eddie, folks; I did not actualy tried what I'm posting here, but I guess it's worth a try. As I see, 'n' in 'c/(x^n)' is a number, right? The HP49G+ does not know it is a number unless you tell it. If I am not wrong (from the excelent HP48G documentation), the recognizable constants are: N1, N2, N3... What about trying 'c/(x^N1)' instead of 'c/(x^n)'? Based on the answer you obtained, Eddie (c*integral(1/(e^(n*ln x)dx), 'n' has been considered as a general variable, that can contain a function. I may also be copletely out of my mind... Cheers. Luiz (Brazil) Edited: 7 Feb 2005, 7:35 p.m.

Re: Trouble integrating on 49g+ Message #4 Posted by JaSon on 7 Feb 2005, 10:09 p.m., in response to message #3 by Vieira, Luiz C. (Brazil) I tried your suggestion of using N1 instead of n and that didn't work, but thanks for the suggestion anyway.

What about n1 instead of N1? (NT) Message #5 Posted by Vieira, Luiz C. (Brazil) on 8 Feb 2005, 2:42 a.m., in response to message #4 by JaSon

Re: What about n1 instead of N1? (NT) Message #6 Posted by JaSon on 8 Feb 2005, 3:16 p.m., in response to message #5 by Vieira, Luiz C. (Brazil) nope tried that too

Re: What about n1 instead of N1? (NT) Message #7 Posted by Eddie Shore on 8 Feb 2005, 11:00 p.m., in response to message #6 by JaSon I tried making N a complex number and it returned 'C*INT(1/EXP(0,3))*LN(Xt)),Xt,X)' Trying IBP (Intergration by parts) gives 'X*N*C*X^N/(X*X^(N*2))' The RISCH function gives 'C*INT(1/EXP(N*LN(Xt)),Xt,X)' This may be a disadvantage of look up tables(?). Just for curiousity, the HP-39 (not G+) returned the same expression.

Re: Trouble integrating on 49g+ Message #8 Posted by J-F Garnier on 10 Feb 2005, 3:25 a.m., in response to message #2 by Eddie Shore If I remember well, integral(c/(x^n)) is -c/(n-1)/x^(n-1) ONLY IF n<>1, otherwise integral is c*ln(x) or maybe c*ln(abs(x)). I'm not expert if HP-49G CAS, but maybe there is a way to add the condition n<>1. J-F

Re: Trouble integrating on 49g+ Message #9 Posted by Raul L on 10 Feb 2005, 2:07 a.m., in response to message #1 by JaSon Alg48, running on my 48GX, gives:-(C/(N-1)*X^(-N+1))

Re: Trouble integrating on 49g+ Message #10 Posted by JaSon on 10 Feb 2005, 12:14 p.m., in response to message #9 by Raul L I haven't use alg48 on a 48 before can you think of any specific settings that are set on your calc?

Re: Trouble integrating on 49g+ Message #11 Posted by Raul L on 10 Feb 2005, 12:44 p.m., in response to message #10 by JaSon Alg48 only needs "exact" arguments. In this case, f(x) is on level 2, the variable X, on level 1, and then INTGR. (If you are interested, Erable -mother of the 49 CAS- is unable to integrate this problem) R Lion

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