Variable X - Dev Hardware

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December 11th, 2008, 01:35 PM

Easy

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Variable X

So I'm working on a program that does certain calculations that require "x" as a variable instead of a stored number.

How can I get the calculator to treat an "x" in something like:

(4x-2)^2

instead of whatever is stored for x?

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December 11th, 2008, 02:50 PM

Airbard

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Use the solve( function under math, to use it solve(equation,variable,guess).

Trader Rating: 0 · #3

December 11th, 2008, 04:41 PM

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Quote:

Originally Posted by Airbard

Use the solve( function under math, to use it solve(equation,variable,guess).

I'm looking to use the derivative function, which is:

Code:

nDeriv(x²,x,2)

(The answer should be 4)

a.k.a

Code:

nDeriv(f(x),x,value of x)

Here's my code:

Code:

:ClrHome
:Output(3,5,"Finding")
:Output(4,7,"the")
:Output(5,4,"Derivative")
:Pause
:ClrHome
:Disp "f(x)?"
:Input A
:ClrHome
:Disp "X?"
:Input B
:ClrHome
:solve(nDeriv(A,x,B)→C
:Disp C
:End

I have highlighted the x variable in red, to show what needs to be a variable instead of a variable.

I'm getting syntax at the ")" after B and before the store arrow on line 7. What am I doing wrong?

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December 11th, 2008, 05:32 PM

Airbard

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nDeriv( is used as an equation in the solve function, so that you still have to define the variable and the guess

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December 11th, 2008, 06:58 PM

Easy

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So the variable would be X, and the guess would be...?

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December 11th, 2008, 07:21 PM

Airbard

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the guess is what you think the answer is
I just realized that the nderiv( function gives a number so the solve( function uses a number as an equation so my suggestion is that you type out the formula for nderiv(
f'(x)=f(x+E)-f(x+E)/2E

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December 11th, 2008, 07:29 PM

Easy

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But the catch is that I'm trying to make this be able to work for any equation, like f(x)=sin(x) @ x=π/2

Sorry for seeming stubborn, but I'm a little noobish/rusty when it comes to stuff like this.

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December 11th, 2008, 07:35 PM

Airbard

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then try using this:

Quote:

:input "EQUATION-"A
:input "GUESS="B
:solve(A,X,B)

where A is an equation
and B is the guess
removing the nderiv( allows any equation to be used

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April 1st, 2009, 09:28 PM

MufinMcFlufin

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Quote:

Originally Posted by Airbard

then try using this:

where A is an equation
and B is the guess
removing the nderiv( allows any equation to be used

No, that won't work
A will be stored as a value still. If you put (X+1)^2 in as A, then it would use the value of X it already has, solve it, and then store that as A
You'd have to store it as a String

Code:

:input "EQUATION-",Str1
:input "GUESS=",B
:solve(Str1,X,B)

This may work, but I don't know, because i have never used solve before. Anyways if you don't know already, you access your list of Strings by pressing [VARS], [7], and then choose which of then 10 you want. Here I used number 1.

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April 16th, 2009, 07:54 PM

gumbee

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Quote:

Originally Posted by MufinMcFlufin

No, that won't work
You'd have to store it as a String

Code:

:input "EQUATION-",Str1
:input "GUESS=",B
:solve(Str1,X,B)

Code:

:input "equation ",str1
:input "guess ",B
:solve(string>Equ(str1),X,B)->C

You have to convert the string to an equation first otherwise the calc gives you a nifty little error.

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April 21st, 2009, 08:20 AM

MufinMcFlufin

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Quote:

Originally Posted by gumbee

Code:

:input "equation ",str1
:input "guess ",B
:solve(string>Equ(str1),X,B)->C

You have to convert the string to an equation first otherwise the calc gives you a nifty little error.

So I'm not the only one who thinks that errors are nifty...
Anyways, I've never actualy done anthing like this, so after looking over my code again before reading yours, I thought something looked wrong, but I never tested it so I just went with it. Does it work now you added that little part?

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April 22nd, 2009, 11:34 PM

gumbee

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no, i had to change some stuff. here's the new code. this is tested and works... well...no errors at least.

Code:

:input "equation ",str1
:input "guess ",B
:string>Equ(str1,Y1)
:solve(Y1,X,A)->C

Y1 is a function variable that can be found buy pushing [VARS] > [->] > [ENTER] > [ENTER]

Last edited by gumbee : April 22nd, 2009 at 11:36 PM. Reason: parentheses mix-up/colors

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April 24th, 2009, 07:27 PM

legoguy314

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I typicaaly input a string, change it to a Y= and store it as Y1 then use seg(Y1,X,X,X) Seq is under list. That mught not be right right but its close, i don't have my calc. with me now so I apologize if that is incorrect

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April 24th, 2009, 07:47 PM

MufinMcFlufin

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Quote:

Originally Posted by gumbee

no, i had to change some stuff. here's the new code. this is tested and works... well...no errors at least.

Code:

:input "equation ",str1
:input "guess ",B
:string>Equ(str1,Y1)
:solve(Y1,X,A)->C

Y1 is a function variable that can be found buy pushing [VARS] > [->] > [ENTER] > [ENTER]

Hold on there, you had it input variable B, but then in the solve code, you used variable A. Was that a typo, or did you intentionally do it? And if so, then why?

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April 25th, 2009, 02:03 AM

gumbee

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Just a typo. Haha.

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