Solving Variable Equations

[DiscoBob]

I can't think of how, and it's really annoying...

example: 2x=4

obviously x == 4

i can't think of exactly how to solve for x though....it's bugging me..i had an idea on it..but then forgot =x


p.s. no, this is not for math homework lol, i dont have math homework XD i'm just curious on how i would do it.

[John]

hm... maybe store the equation as an array, use regular expressions to parse the degrees and coefficients, store each as a variable and use mathamatical operators to do the work

or if its a simple equation like that u could use a loop, but that wouldnt work that well with irrational equations or more complex ones

im interested in hearing some other ideas

[TcM]

Umm sorry mate but if

2x=4
then x=2

huh?

[Jimbo]

Originally Posted by Tcm9669

Umm sorry mate but if

2x=4
then x=2

huh?

Thats exactly what I was thinking?!!

[Lop]

hehe, that is what I was thinking.

So you have 2x=4 which means x=2? How do you have that in your code? Is it a string?

$variable = "2x=4"?

I do a substr on it, pull out the 2 and the 4 by getting the index of the X and the =. Once that is done, divide 4 variable by 2 variable.

[John]

Originally Posted by Lop

hehe, that is what I was thinking.

So you have 2x=4 which means x=2? How do you have that in your code? Is it a string?

$variable = "2x=4"?

I do a substr on it, pull out the 2 and the 4 by getting the index of the X and the =. Once that is done, divide 4 variable by 2 variable.

sort of what i was saying, but i was thinking suppose the equation is dynamic and dependent on what the user enters. he can enter any degree equation and any ammount of terms he wants.

i suppose you could explode it at the equals sign then subtract the right side of the equation from the right side of the equation and set the equation equal to zero. from there you could apply the intermediate value theorum and newtons method (farly basic calc theorums) and iterate it a hundred times or so, if the output appears chaotic there is no answer ie) X^2 = -4 has no answer and the iterations will appear chaotic... if the iterations appear as an integer or appear to approach a single value (rational or irreational) that value is the answer... fairly complex process and would also require taking the derivitive of the equation which would require a complex algorythm in itself... but i suppose this would be the "fool proof" way of going about it..

edit
hell on second thought X^2 = -4 does have an answer 2i^2 but that would require another step to the program, but its seems pretty straight forward other than a bunch of checks/validations and indepth calculations... and since im learning java in my computer science class i may try to program this in java for fun because im weird like that

[Jordan]

How would the user be inserting the code? A textbox?

Logic wise you could have 4 text boxes and one combo box. The first text box they would enter X (using your X^2 equation), combo box select ^ (or * or /), 3rd enter 2, fourth and equals enter -4. You could then take the opposite of the combo box selection and figure out the rest using the textbox variables.

[TcM]

Hmm its a little complicated!!

[WingedPanther]

For exact solutions: you are going to be limited to 4th degree equations. 5th degree equations, in general, do not have a closed form solution, though they can be approximated using Newton's Method. You can find information about general solutions to cubic and quartic solutions here. Mind you, those solutions may be integers but look like messy complex numbers.

[DiscoBob]

lmao..i can't believe i messed up that first answer XD i must've been thinking i was typing the equation not the answer ::blushes::

all this seems interesting and i will still eventually work on it when im not so busy working on my forums...but thanks for all the info

and es..the user would just enter in an equation in a textbox