# Basic Entry - Help Needed With Variables

### #1

Posted 30 April 2009 - 04:24 PM

This is my first post. I'm studying electrical engineering.

My Classpad 330 is a giant step up from my old FX-115!

Please help me to understand the order of entry: I'm trying to input an equation with a variable. I'd like to change the variable and get a new output. Unfortunately, I'm doing something wrong.

Ex. (2X^2-8)/(x^2-1)

Can I just change the variable, then re-execute the equation for a different output? I also have to remember to input a negative number in parenthesis before squaring it. (-3)^2 is not -3^2.

If you have any other helpful advice, please tell me.

Thanks in advance,

Rob in Ohio

### #2

Posted 30 April 2009 - 05:16 PM

Yes, you can change the value assigned to the variable and then recalculate by highlighting the first value, changing the value, and then pressing EXE. The ClassPad will recalculate all expressions until it reaches the end. Or, you can press the icon of one finger and calculate only the row the cursor is in.

In your example, you have an upper case x and lower case x. Those are considered different variables in the ClassPad. If that was just a typo, the order looks fine.

When I enter equations, I use the keyboard's 2D tab and enter them the same as how they are in a textbook, especially if they are complicated. If you have ClassPad Manager, you can enter the equation with 2D, highlight the equation, copy, and then use Paste Special from the right click menu. When the equation is pasted into the window, it is in single line form with the parenthesis where they should be. With the handheld, you could open the Graph application within Main or eActivity, drag and drop the 2D equation into the Graph applications text box and also see the equation in single line form.

3⇒x 3

(2*x^2-8)/(x^2-1) 5/4

2*x^(2-8)/x^(2-1) 2/2187

2⇒x 2

(2*x^2-8)/(x^2-1) 0

2*x^(2-8)/x^(2-1) 1/64

My advice would be to explore the ClassPad, manual, and forums. Have fun with it! And good luck in your studies!

Debbie

### #3

Posted 01 May 2009 - 04:41 PM

It is excellent to see that we have a new classspad owner on the forum

I have a simple answer. There are many ways you can acheive what you are asking. One is to use

**functions.**You can stor an equation such as 5x+3 into a function. Then you can use the f(x) or g(x), etc notation. You define a function usine the command Define. You can find it in the Action -> Command -> Define. In your case you would use:

Define f(x)=(2x

^{2}-8) / (x

^{2}-1)

then type the command f(2).

Then this will give you an output. To change that output, simple highlight your equation and clear the function 'x' value. Type a new value and you will get a different output.

You can also highlight the f(something) and Drag+Drop to the next line, then change the value.

Regards,

I wish you luck with your new machine

mintsmike

**Edited by mintsmike, 01 May 2009 - 04:42 PM.**

### #4

Posted 02 May 2009 - 01:55 PM

A quick solution to your problem would be to use the | operator. It's pretty useful when you don't want to use variables or declare functions.

(2x^2-8)/(x^2-1)|x=2

This will return the value of the expression when x=2. You can find "|" in the OPTN part of the "mth" tab.

### #5

Posted 06 May 2009 - 10:05 PM

Thank you for your help. This is a great forum and the Classpad 330 is an excellent calculator. I really like the different ways to solve the same problem that I was having. Thank you.

Kilburn, I'll start C++ programming in a couple of quarters.

Mintsmike, where can I find those options? Where is that in the manual? (at 941 pages, it's easy to miss some sections) I'd like to try your idea also.

Thanks again!

### #6

Posted 07 May 2009 - 06:17 AM

Hi there. I dont quite know what you mean by 'options'.Everyone,

Thank you for your help. This is a great forum and the Classpad 330 is an excellent calculator. I really like the different ways to solve the same problem that I was having. Thank you.

Kilburn, I'll start C++ programming in a couple of quarters.

Mintsmike, where can I find those options? Where is that in the manual? (at 941 pages, it's easy to miss some sections) I'd like to try your idea also.

Thanks again!

For the manual. Get the CP300+ manual. It should be 753 pages long. Then go to page 543. All your information is on there

Regards

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