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Problem with equations like ax^2+bx+c = 0


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#1 Chapas

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Posted 28 June 2004 - 03:20 PM

How can i resolve a equation like : ax^2+bx+c = 0 , in my cp300 ??


I put some equantion in solve, and some results are correct others are wrong !! :blink:


Could anybody explain to me what is going wrong ?

#2 Overlord

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Posted 28 June 2004 - 03:42 PM

can you give an example of equation and results ?

check also that your variables haven't wrong values in memory..

#3 SoftCalc

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Posted 28 June 2004 - 05:37 PM

Try clearing all variables first by entering Clear_a_z. If this doesn't work give some examples...

#4 Chapas

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Posted 28 June 2004 - 07:07 PM

Another question

When we put in SOLVE MENU the equation x^2-4 = 0 , the result should be x= -2 and x=2 , but in result oly appears x=2 , WHY :blink: ??

#5 Daruosh

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Posted 28 June 2004 - 07:56 PM

When we put in SOLVE MENU the equation x^2-4 = 0 , the result should be x= -2 and x=2 , but in result oly appears x=2 , WHY  :blink: ??

I get {x=-2,x=2}

try solve(x^2-4=0)

#6 Chapas

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Posted 28 June 2004 - 08:06 PM

In Main Menu i appers {x=-2, x=2} !!

But why don't appers the same in the solve menu ?

#7 SoftCalc

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Posted 28 June 2004 - 08:24 PM

In Main Menu i appers {x=-2, x=2} !!
But why don't appers the same in the solve menu ?

What do you mean by "solve menu"? Do you mean the NumSolve application? If so, the NumSolve application solves numerically, not symbolically. You won't get all roots. There is't even a guarantee you'll get an exact solution.

In the NumSolve application you have to give an initial guess (x=) and it will attempt to find the closest solution. Enter x=1 and it will find the solution x=2. Enter x=-1 and it will find the solution x=-2.

If you want a complete, symbolic solution you should try using "solve(" in MAIN first.

#8 Overlord

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Posted 28 June 2004 - 08:43 PM

i think the numeric solver uses a newton raphson method (or a variant like the secant method) that tries to find the nearst root from the begin point (numerically so not the exact value).

=>
1. it can found only 1 value at one time
2. you can't be sure it will find a solution even if there are solutions (for a success with n-r you must satisfy a mathematical condition ; most time it will be satisfied if your guess is relatively "close" to the solution or if the function is "regular" enough
3. sometimes it can give a erratic solution... don't forget to check the solution

but, it can estimate solutions that the calc or even we can't find by symbolic methods :)

(and it can also be useful for teachers to test the students at an numeric methods exam :-/ grrrrr...)

#9 R00KIE

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Posted 02 July 2004 - 11:24 AM

But don't underestimate the power of the numeric solvers because when you can't solve it in exact/symbolic mode you need to turn to numeric mode.

#10 SoftCalc

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Posted 02 July 2004 - 04:51 PM

I totally agree. I calculator wouldn't be a calculator if it didn't have a good numeric solver, and Casio's root solver does an excellent job. :thumbsup:

I just wanted to make the point that a numeric solver isn't guaranteed to get a correct solution. People often expect that a calculator must always give the correct answer or it is some type of bug. A numeric root solver is just riding the curve trying to find the answer.




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