(1>x) => (x<1)

[compsystems]

Hello

solve((5<(-2*x+7))AND ((-2*x+7)≤11),x,'=' ); [Enter] returns (x≥-2) and (x<1)
but -2≤x<1 [Enter] returns (x>=-2) and (1>x)


is it possible to improve the results of mathematical expressions as they appear in textbooks?
(x>=-2) and (1>x) => (x>=-2) and (x<1)

[parisse]

Evaluation replaces < and <= by equivalent > and >=, in order to have a smaller number of cases for further processing (e.g. in solve). The result of solve is not evaled, that's why < and <= are not translated.

[compsystems]

Having a smaller number of cases for further processing is good from a computational point of view, but not from the point of view of teaching and learning mathematics, because textual mathematics follows writing rules.
In addition to spending more time, with current binary processors, that time to display expressions like in textbooks would not affect much.

Another issue that is important is to show the results with the OR or UNION operator, to differentiate types of solutions.

solve((-4)≥(-2*ABS(3*x+1)),x ); => [x≤-1, x≥1/3] =>(x≤-1) OR (x≥1/3) =>(x≤-1) UNION (x≥1/3)

and the following case express it as x≠5

solve((ABS(x-5))>0,x); => [x<5,x>5] => x≠5

finally a function to convert a three-part inequality or similary to separate expressions and vice versa. I don't know what name it could have.

f(-2≤x<1) => (x≥-2) AND (x<1) => (x≥-2) INTERSECTION (x<1)
f((x≥-2) AND (x<1)) => '-2≤x<1'
f( (x≤-1) OR (x≥1/3)) =>(x≤-1) UNION (x≥1/3)
f(x≠5) => x<5 or x>5

[parisse]

Sorry, but that's not work for me for two reasons: first I don't have time to do that, second I don't share the vision that using a CAS in education means we should mimic textbooks. My point of view is that the students should learn how to use a CAS, and therefore understand that for example the answer of solve is a list of possible values. Otherwise, the student is not the brain who is conducting computations, he becomes the slave of an user interface.

[compsystems]

Adding new rules to the Xcas kernel should be an easy job in words but in practice it requires many hours of work and movement of neurons that very few have. There are very few CAS programmers in the world and my brain is not at that level. I would like to have the power to access the source code and contribute.

Regarding the use of CAS, it is clear that it can be manipulated as is, but I have seen that mathematics is not liked by the majority of students who study engineering, this is an irony, because its language is complex, it is like learning a second language, something also statistically complex for most people.

I think that if a 'CAS' is closer as shown to the mathematicas textbooks it would motivate us to use it with more apprehension, when things change the brain 'runs away'

[XcasEngGuy]

I have done a lot of work (programming in Xcas and cygwin) to make the output from Xcas more understandable to students. Intermediate steps in the Algebra and Calculus seemed more important to students.