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CAS: solve without simplify fails
07-10-2017, 04:11 PM
Post: #1
CAS: solve without simplify fails
Please excuse me if this has been answered here before. I couldn't find any thread referring to this yet.

In CAS:
solve((x-7)*(x+7) = x^2 - 49) --> [undef]

solve(simplify((x-7)*(x+7) = x^2 - 49)) --> {x}

Firmware: 20160829 (10637)

Please understand that for pupils it is hard to enter nested commands. Is there any other way to solve this directly?

Many thanks in advance.
Bruno
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07-10-2017, 05:05 PM (This post was last modified: 07-10-2017 05:28 PM by compsystems.)
Post: #2
RE: CAS: solve without simplify fails
is very interesting that with the simplification of the expression, Xcas can calculate it, the good thing that Bernard Parisse (BP), could improve the command to solve without needing to simplify

{X} means that x = x, that is, it takes all the values of the real numbers

https://www.wolframalpha.com/input/?i=so...%5E2+-+49)

[Image: casio_classpad_on_pc_image00.png]


(07-10-2017 04:11 PM)whilealive Wrote:  P.. for pupils it is hard to enter nested commands.
Standard notation not RPN or PN involves nesting orders (cmds) within orders

.
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07-11-2017, 01:11 PM
Post: #3
RE: CAS: solve without simplify fails
Normally you don't need to simplify before solving. But here there is special code to solve linear equations a*x+b=0 and it does not contain simplification for a, I will improve that. Never seen this before, because nobody ever tried to solve 0=0 with that kind of input.
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07-11-2017, 06:55 PM
Post: #4
RE: CAS: solve without simplify fails
Great. Thanks for looking into it.
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07-11-2017, 07:33 PM (This post was last modified: 07-11-2017 08:09 PM by compsystems.)
Post: #5
RE: CAS: solve without simplify fails
A similar expression

solve( x^(x^x)=(x^x)^x, x)
list[ 2.0 ]

"Unable to isolate ... hp-prime
Root x = 1 was not found on Xcas, please show "More solution may exist"
https://www.wolframalpha.com/input/?i=so...x)%5Ex,+x)

solve(sqrt(x)^x=x^sqrt(x),x)
"Unable to isolate ... hp-prime
list[1.0,4.0] Xcas
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07-12-2017, 05:39 AM
Post: #6
RE: CAS: solve without simplify fails
Of course more solutions may exist, since bisection may skip over one solution if the step between 2 evaluations is too large.
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