22 replies to this topic

[DigitalOD]

Im really disapointed that the classpad cant solve non square simultaneous equations , and the voyage and 49g can, this really sucks. If anyone can help me how to solve something like this in the classpad will give me a really big hand.

2x + 3y = 4
3x + 2y = 6
3x + 4y = 7


Thanks

[SoftCalc]

I'm not really sure what you are trying to solve. As far as I can tell, there is no solution.

I tried this on my HP49 (actually the HP49 emulator ) and, as expected, it will not solve symbolically because there are more variables than equations.

If you have three equations and two unknowns you either have a duplication equation in disguise, or there is no solution. If you have a duplicate equation it means that one of the equations is either a multiple of another, the sum/different of the other two, or a combination of both. The way to test for this is to solve two of the equations and see if this solution satisfies the third. If you get no solution when solving two of the equations you were unlucky and picked the "duplicate" equation. Solving a different pair should give a solution. Finally, plug the answer into the remaining equation. If it solves then you have a solution. Otherwise there is no solution.


The ClassPad can solve...

2x + 3y = 4
3x + 2y = 6

...and get the solution {x=2,y=0}. This solution does not solve the third equation, which means there is no solution.

[MCFONG]

Another good way is to graph three equations as it is so easy to do in CP300. Go to eActivity, open a graph window and enter all three equations and drag drop them into the window...clearly you see that there are solutions for any 2 of these equations but not all 3.

MCFONG

[The_AFX_Master]

digitalOD your question haven?t sense.....3 equations with 2 guesses,the determinant of the coefficient matrix is 0, you have 2 options

.-Z coefficient is zero in all three equations, the calc must returns a MA ERROR

.- 2 of 3 equations are linear independendt, use only this two equatios that have coefficients that form a non singular matrix. the other equation is a linear combination of the previous ones..

[PAP]

The system that digitalOD gives has no solution indeed. However, ClassPad should be able to detect that, by answering something like "No Solution", instead of "Invalid Dimension". Clearly, solve works if and only if the list of the equations and the list of the unknowns have the same size.
On the other hand, a system with less equations than unknowns can be solved in ClassPad very easily. For example, the system
x+y+3x=3
x-2y-3z=6
has infinite solutions. In ClassPad, you simply use
solve({x+y+3z=3,x-2y-3z=6},{x,y})
and you get the correct solution.

[SoftCalc]

The system that digitalOD gives has no solution indeed. However, ClassPad should be able to detect that, by answering something like "No Solution", instead of "Invalid Dimension".

Hmm, In the general case is it "No Solution", or could this be an entry error. Imagine someone enters three equations in x,y,z and only two variables (x and y) to solve for. It could be that they simply forgot to enter the 3rd variable and it is, in fact, a simple entry mistake. In this case "No Solution" would make them think they entered everything find and there is simply no solution. On the other hand, "Invalid Dimension" is a bit confusing and isn't completely correct either.

I can see that solve is a little different from most commands that need correct argument count matching though. I can see where something like the following should solve.
solve({x+y=2, x-y=5}, {x,y,z}) {x=7/2, y=-3/2, z=z}
...or even...solve({x+y+z=2, x-y=5+z}, {x,y,z}) {x=7/2, y=-3/2-z, z=z}

[PAP]

Hmm, In the general case is it "No Solution", or could this be an entry error. Imagine someone enters three equations in x,y,z and only two variables (x and y) to solve for. It could be that they simply forgot to enter the 3rd variable and it is, in fact, a simple entry mistake. In this case "No Solution" would make them think they entered everything find and there is simply no solution. On the other hand, "Invalid Dimension" is a bit confusing and isn't completely correct either.

Maybe a warning message (something like :"Possible entry error: 3 equations and 2 variables" - maybe something shorter) and a "No Solution" (or the solution, if it exists) is the correct answer (btw, Mathematica does not print any warning).

[SoftCalc]

(btw, Mathematica does not print any warning).

<{POST_SNAPBACK}>

Maple 7 simply returned a blank line.

[unique33]

maple 9.5

> eqns := { 2*x + 3*y = 4, 3*x + 2*y = 6, 3*x + 4*y = 7 };
eqns := {2*x+3*y = 4, 3*x+2*y = 6, 3*x+4*y = 7}
> [solve( eqns, {x, y} )];
[]

because the determinant is zero and no solutions exist.
If you want to be sure that no solutions exist in maple add [ , ] before and after the solve statement .

[jps]

I found a system that it should solve but it doesn't
try this: solve({y=x^2,y=x},{x,y})
it should output 2 points, something like x=0 and y=0 or x=1 and y=1
all it outputs is: {y=x^2,y=x}

whats wrong? the ti-89 can solve this, I tried

[Lovecasio]

Hi.
Nothing is wrong. That 's just because ClassPad cannot solve non-linear system of equations automatically. I don't know whether it is available in OS 3.0.

[MicroPro]

The ti-89 can solve this, I tried

TI 89 or its emulator?

[jps]

The emulator, but it's using the upgrade rom downloaded from official TI site, so it should be exactly the same on the calculator

[jps]

OS 3.0?!? where did you get that? has it been officially released?

[-Tom-]

I have seen OS 3.0, and it can do this. I don't know about OS 2.0...

Where we can see it also?

[The_AFX_Master]

OS 3.00!!!!!!! WHERE?.... Softcalc, do you know anithing about the releasing of OS 3.00?? (redundant question )

the men that seen the os 3.00? how many changes?...any big surprise??? thanks a lot

[betoe]

Please dont believe (also deny) at 100% posts like "I have seen OS 3.0, and it can do this. I don't know about OS 2.0..." . We must wait for a official release, no one can send it to us (if its finally made), maybe it was a beta version, who knows...

[SoftCalc]

I found a system that it should solve but it doesn't
try this: solve({y=x^2,y=x},{x,y})
it should output 2 points, something like x=0 and y=0 or x=1 and y=1
all it outputs is: {y=x^2,y=x}

Is this right? I think it should solve. What version of the OS are you using? Has anyone tried this in OS 2.2? (I would try it but it's hard for me to be sure I have a clean version of OS 2.2 )

As far as this solving in OS 3.0, I can confirm that is does. OS 3.0 has a number of improvements to non-square simultaneous equations.

Still, I think this should solve in OS 2.2

[jps]

yeps, that result is with os 2.2, checked just now.
Any release dates for os 3.0?

[SoftCalc]

Any release dates for os 3.0?

Even if I though I knew, I wouldn't really know.

[MicroPro]

Can't we directly ask CASIO?