hp prime calculator Cannot Solve simple equation

[ragoreco]

Hello,

I'm trying to solve

 solve( (2)^x = (x)^2,x)

But the calculator cannot solve or am I doing somthing wrong?.

I lost my TI Nspire CX and I though that HP Prime, since is a recent modern version, were able to solve something simple as that, I am wrong. (TI Nspire solved it ).

How solve the above equation using the HP Prime? I'm seriusly thinking to return this back.

Thank you

[dulcimoo]

I got -0.766665695962

That seems to be right.

While I work for HP (Not the Calculater Division) ... I'm only typing for myself here.

[ragoreco]

Hey good job Dulcimoo!!!

Did you find the other two roots? there are three. How much work did you do to get that root? did you use solve(f(x),x) or the zero function? or you just strugle trough bunch of procedures.

I realize that HP prime still using HP 50g firmware,  it seems to me that HP Prime is just HP 50g with makeup, I recall I had same issue solving the equation with it.

Try: https://www.wolframalpha.com/input/?i=solve%282^x+%3Dx^2%2Cx%29

[Joe_Horn]

Since you want approximate solutions, use the fsolve command, not the solve command:

fsolve(2^x=x^2, x, 0) --> -.766664695962

The 0 at the end is the initial guess; the solver looks for a solution close to that.  Instead of an initial guess, you can also specify either an interval or a list within which to find a solution:

fsolve(2^x=x^2, x, 1 .. 3) --> [2.]

fsolve(2^x=x^2, x, { 3 5 }) --> [4.]

> I realize that HP prime still using HP 50g firmware,  it seems to me that HP Prime is just HP 50g with makeup...

No no no, that's not true at all.  None of the 50g firmware is in the Prime.  They had to rewrite everything from scratch, since there is no RPL kernel in Prime.  The math library that's used in the Home environment (for normal number crunching, not solving) was written to obtain the same famous 12-digit BCD accuracy as the 50g, but it was all new code.  However, the solvers and the other CAS operations in Prime are not based on the 50g at all, but are all new, based on the very robust Xcas computer software package.

[ragoreco]

Good job Joe,

I see, fsolve is one way to go, thank you.

I think then something is wrong with my calculator or there are some settings hidden somewhere that I need to change.

I tried using the fsolve you used, I typed the first equation as you showed ... comes back as "undef"

I look for the fsolve in the user guide, it doesn't mention anything about lists anywhere. I tried the other fsolve you mention, with list and interval:

fsolve(2^x=x^2, x, 1 . . 3) --> Error: No significant digits in number

fsolve(2^x=x^2, x, { 3 5 }) --> undef

Actually the space between 3 and 5 is understood as multiplication 3 * 5.

Since the last one uses { .. } as list entry and it is not documented in the user guide, I assuming is not implemented in the firmware. Can you point me where did you find that list is one option?.

I  tried the example in the user guide:

fsolve(cos(x)=x,x,-1..1,bisection_solver) --> Error:Two decimal separators in input

Introducing a space after -1 and space between dots and in front last 1 comes back with: Error: No significant digits in number.

Well it seems that this calculator is not working well. Joe, do set any flags?

Thank you

[ragoreco · Accepted solution]

After I played with the calculator I found that it has to be in  CAS environment in order for the solver to work, if the fsolve is used in Home environment it won't work:

fsolve(2^x=x^2, x, -10 . . 10) --> [-.76664695962 2. 4.]

nSolve worked too, but it doesn't allow an interval.

So the solution is that those commands need to be used in the CAS environment.

Thanks

[Joe_Horn]

Oops!  Quite right.  In general, all symbolic math work should be done in the CAS; that's what it's for.  Home is intended for ordinary number-crunching, not symbolic math.  Sorry for not pointing that out.