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CAS: solve solutions - compsystems - 08-25-2016 07:18 PM
hp-prime
solve(((x+5)*e^x) = ((x+5)*e^(2*x))) [ENTER] returns ->
{0} // one answer
why the CAS returns only one answer?
Expanded form
expand( (x+5)*e^x) = (x+5)*e^(2*x) ) [ENTER] returns -> x*e^x+5*e^x = x*e^(2*x)+5*e^(2*x)
mathematica returns 3 answers
https://www.wolframalpha.com/input/?i=(x%2B5)*e%5Ex+%3D+(x%2B5)*e%5E(2*x) [ENTER] returns ->
x = -5 // real solution
x = 0 // real solution
x = 2*π*i*n where n ∈ Z // a symbolic answer =]
RE: CAS: solutions - Steve Keeley - 08-25-2016 08:22 PM
I tried it (with different parentheses) and, after a cryptic warning, got the same answer Mathematica did.
RE: CAS: solve solutions - retoa - 08-26-2016 07:49 AM
Hi Steve!
(08-25-2016 08:22 PM)Steve Keeley Wrote: I tried it (with different parentheses) and, after a cryptic warning, got the same answer Mathematica did.
How did you write it to obtain the full answer?
I get the same result as compsystems
RE: CAS: solve solutions - Dirk.nl - 08-26-2016 01:12 PM
Have you select Complex? (CAS settings)
I have the same answer as Steve (10077)
RE: CAS: solve solutions - compsystems - 08-26-2016 01:17 PM
but the answer (-5) is not complex output is real number
RE: CAS: solve solutions - Dirk.nl - 08-26-2016 01:50 PM
Have you try it?
Deselect complex, answer is {0}
Selected complex, answer is {-5 0}
RE: CAS: solve solutions - Tim Wessman - 08-26-2016 03:20 PM
Specifying a range works here as well.
-10..10 returns -5,0 also
Perhaps bernard can shed some light as to why it only finds the one solution in this case without specifying a range.
RE: CAS: solve solutions - Steve Keeley - 08-26-2016 10:07 PM
(08-26-2016 07:49 AM)retoa Wrote: Hi Steve!
How did you write it to obtain the full answer?
I get the same result as compsystems
solve((x+5)*e^x = (x+5)*e^(2*x),x)
(note that on the calculator I didn't have the parentheses around the 2*x term since in textbook form it was obvious that the whole term was part of the power of e)
My settings were Exact on, Complex on, Use Sq on, Use i off, Principal off and increasing off.
The warning I got was:
Warning: solving x in equation
-x*(e^x)^2+x*e^x-5*(e^x)^2+5*e^x=0
-x*(e^x)^2+x*e^x-5*(e^x)^2+5*e^x=0
Anybody know what this warning means?
RE: CAS: solve solutions - retoa - 08-26-2016 10:37 PM
Right, with complex on it gives both answers.
Does it need to use complex numbers for some substitution?
RE: CAS: solve solutions - parisse - 08-27-2016 06:16 AM
With the current version of Xcas I get -5 and 0 for solve((x+5)*e^x = (x+5)*e^(2*x),x). I don't know why it does not work for older versions of giac.