## What does "a constant is invalid as a variable"...

by:

Here are some examples illustrating this problem
```
> x:=3;
...various other calculations, during which you forget that you
gave x a value
> solve(2*x=1,x);
Error, (in solve) invalid arguments

> plot(2*x,x=-1..1);  No complaint is written out, but the plot is
just the line y=6.
```
Here x already equals 3, so it doesn't make sense to use it in an assertion like "2*x=1", and plotting "2*x" is just plotting "6". Just as the above section shows an example of having too many indeterminates, this example shows what happens when there are too

## Why doesn't my function definition work?

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Here are two correct ways to define functions.
```
> f:=2-x;           One way is by assigning a formula to a name.
> plot(f,x=-1..1);  If you use this method you can refer to f,
> solve(f=0,x);     BUT referring to "f(x)" yields nonsense.
> f(x);      WRONG
2 - x(x)

> f:=x->x^2;          Another way is by using an arrow.
> f(x);               If you use this method you can refer to f(x),
> f(1);               BUT referring to just "f" only yields "f",
> plot(f(x),x=-1..1); not the function.
> solve(f(x)=0,x);
```

## When I enter the same command repeatedly, why...

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Some commands change the internal state of the calculation, so the results have to be different each time. For example, if x is 1, entering x:=x+1; repeatedly obviously yields values of x that count up. A less obvious way that a command can do different things different times it is used is if it includes the % reference to the previous result. Then, the result from the command will depend on what the previous result was. It is less confusing to assign a name to a result you want to use again, rather than referring to it with %.

## How do I undefine a variable to put it back to...

by:
To undefine x, enter x:='x'; To restart Maple with its memory cleared, enter restart.

## Basic Maple Commands

by:
Help with using the simple Maple Commands

## Help with Plotting

by:
Any questions that apply to plotting in Maple will appear here.

## Why did my graph turn out empty or blank?

by:

A1: You forgot to specify a range on the independent variable.

``` > f:=2-x;
> plot(f);              WRONG
Plotting error, empty plot
> plot(f,x=-1..1);      RIGHT
```

A2: You might be plotting a quantity that isn't defined. For example, you might have defined Y but then asked Maple to plot y. Maple is case-sensitive, and many strange behaviors are the result of typing a variable name in the wrong case.

Another way a plotted quantity can be undefined is if you didn't use the assignment operator := to define it.

``` > y=sin(x);              WRONG
```

## I opened a worksheet that I saved before, but...

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When you open a Maple worksheet you must execute it to get the variables defined. You can do this by stepping through the commands from the beginning, or by clicking on the execute all button on the toolbar which looks like this, !!!

## How do I print my session?

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Click on "File" and select "Print" from the menu.

## How do I get the program to give me help I can...

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Instead of trying to follow the numerous Help menus, try entering ?topic to go directly to the help page you want. For example, to get help with the int (integration command), enter ?int at the Maple prompt. You will working examples for each command at the bottom of the help page for the command.

## I am a new Maple user and I do not know how to...

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Maple's syntax is very intuitive and not complicated. The best way to learn how to use Maple is to take The New User's Tour . The New User's Tour presents the fundamental Maple commands that every user should be aware of. The tour covers many areas of Maple, including: The Maple Worksheet Environment, Numerical Calculations, Algebraic Computations, Graphics, Calculus, Differential Equations, Linear Algebra, Finance and Statistics, Programming, and Online Help. The tour is easy to proceed through, and it can take up to two hours if all topics are examined. In order to start The New User's Tour you should go to Help --> New User's Tour .
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