Close down Maple, and using your file navigator, go to the directory that you unzipped the files to.  Double click on one of them to open it with Maple.  See if it executed without any errors.  If it does, then there is an issue with your path.  One thing you can do is create a blank worksheet and save it in the same directory as the files that you just unzipped.  Then the commands from the local lib files will be available to your worksheet.  Don't forget to load the plots package "with(plots)" when using the display command.

The attached worksheet was created with Maple 12 Classic Interface.  The Standard Interface does the same thing.  Did you define one variable and not the other in your worksheet, and then reuse it elsewhere?

Download 221_alphadelta.mws

plot( .8*theta+.87, theta=(160/180)*Pi..(330/180)*Pi,coords=polar,style=line,linestyle=dot,thickness=6);

?plot,options

will bring up the help page that describes the above, and more in detail.

You can do both.  I showed you how to do this here.

Here is an example.  You can also do this using the methods from the other posting, but this will show you how to use some of the other commands.

restart: with(plots):

plot(x^2-4,x=-4..4,color=blue);

solve(x^2-4,x);

pointplot([[-2,0],[2,0]],symbol=circle,symbolsize=25,color=red);

display(%,%%%);

The display command combines more than one plot.  The % and %%% tell the display command to combine the previous result, and the 3rd previous result.

You could also do it like this.  Notice that there is a semicolon at the end of the plot commands once they are assigned to a variable.

xx:=plot(x^2-4,x=-4..4,color=blue):

yy:=pointplot([[-2,0],[2,0]],symbol=circle,symbolsize=25,color=red):

display(xx,yy);
 

Now modify the above for your own function and see what happens.

See help pages:

?Student[Calculus1][FunctionChart]

or

?Student[NumericalAnalysis][Roots]

Your answer has real parts, and imaginary parts.  Maple expresses imaginary numbers by  appending an "I" after them.

For example, if you wanted to declare an imaginary number, you would do it as:

3+3*I;

For more help on this, type:

?I

and hit the enter key.

What else do you have in your worksheet before this?  Has the variable "x" been defined with units prior to your plotting command?

Open the attached worksheet.  Do you still get the same error?

View 221_plot_error.mw on MapleNet or Download 221_plot_error.mw
View file details

You can save your worksheet with the error message, and use the green up arrow to upload your file.

?diff

?solve

diff will give the derivative of your function.  solve will find the values of c of the 4th order equation.  Start with the help page for each of the commands above.  There are examples there that you can modify for your own function.

restart:with(plots):

n:=2:

S[1]:=piecewise(1<=x and x < 2,1,-1);

S[2]:=piecewise(1<=x and x < -2,2,-2);

.

.

S[n]:=

display(seq(plot(S[i],x),i=1..n));

The code example from above works fine without any errors.  Did you cut and paste, or did you type it in?  Here is a worksheet that is identical to what was posted by Robert Israel.

Download 221_dfi.mws

Here is an example from the help page for DEplot, using your differential equation, without initial conditions.   Is this what you are looking for?

restart:

with(DEtools):

eqn:=diff(  y(x) ,x )=1+y(x)^2*x;

DEplot(eqn,y(x),x=-1..1,y=-1..1,arrows=medium);

See also:

?DEtools[dfieldplot]

?DEtools[phaseportrait]

See the help for the translate command, which is part of the plottools package.

?plottools[translate]

Try this link, from a previous thread, dealing with the same topic.

Start here, and see if you can modify the worksheet examples to suite your needs.   Another option is to use implicitplot with the option filled=true.  See the help pages for implicitplot.  ?plots[implicitplot]