Trouble integrating on 49g+ « Next Oldest | Next Newest »

 ▼ JaSon Junior Member Posts: 42 Threads: 23 Joined: Aug 2007 02-07-2005, 12:13 PM 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? ▼ Eddie Shore Senior Member Posts: 260 Threads: 40 Joined: Jan 1970 02-07-2005, 03:15 PM 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) ▼ Vieira, Luiz C. (Brazil) Posting Freak Posts: 4,027 Threads: 172 Joined: Aug 2005 02-07-2005, 07:34 PM 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. ▼ JaSon Junior Member Posts: 42 Threads: 23 Joined: Aug 2007 02-07-2005, 10:09 PM I tried your suggestion of using N1 instead of n and that didn't work, but thanks for the suggestion anyway. ▼ Vieira, Luiz C. (Brazil) Posting Freak Posts: 4,027 Threads: 172 Joined: Aug 2005 02-08-2005, 02:42 AM ▼ JaSon Junior Member Posts: 42 Threads: 23 Joined: Aug 2007 02-08-2005, 03:16 PM nope tried that too ▼ Eddie Shore Senior Member Posts: 260 Threads: 40 Joined: Jan 1970 02-08-2005, 11:00 PM 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. J-F Garnier Senior Member Posts: 412 Threads: 40 Joined: Mar 2006 02-10-2005, 03:25 AM 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 Raul L Junior Member Posts: 5 Threads: 0 Joined: Jan 1970 02-10-2005, 02:07 AM Alg48, running on my 48GX, gives:-(C/(N-1)*X^(-N+1)) ▼ JaSon Junior Member Posts: 42 Threads: 23 Joined: Aug 2007 02-10-2005, 12:14 PM I haven't use alg48 on a 48 before can you think of any specific settings that are set on your calc? ▼ Raul L Junior Member Posts: 5 Threads: 0 Joined: Jan 1970 02-10-2005, 12:44 PM 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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