Problem calculating an expression with roots

[parisse]

(02-02-2015 11:49 AM)retoa Wrote:  By the way I don't work in an american school, I live in Switzerland, but I think the problems with roots and fractional exponents are the same worldwide.

I don't think it's worldwide. I do not remember having to play with that kind of exercices in France. And it is perhaps because it does not bring anything more than playing with integral powers to understand power rules, while adding artifical complexity because the expression is not defined for all values of x (or ambiguous like the definition of x^(1/3) for x<0).
As I said, I'm not against improving the CAS with heuristics like that if it's not too hard to implement (and fortunately this one is not too complicated to implement), but I can't guess all kind of purely artificial/academic exercices and I don't think a CAS should have this as a priority, a CAS should concentrate on algorithms not heuristics.

lrdheat:
For the differential equations, I don't understand where there are too may constants, a first order equation has one constant of integration, a second order two constants. Or maybe you speak about linear differential equations with constant coefficients, where Xcas returns the general solution expressed with special constants: the value of the function and derivatives at x=0, in other words initial conditions at x=0. Then you may find there are too many time the same constant because you are used to express the general solution without connection to initial conditions.