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?
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)
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.
I tried your suggestion of using N1 instead of n and that didn't work, but thanks for the suggestion anyway.
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.
Alg48, running on my 48GX, gives:-(C/(N-1)*X^(-N+1))
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
I haven't use alg48 on a 48 before can you think of any specific settings that are set on your calc?
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