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\Large
\noindent
Three last things:

(1) If the file says to install a graphics package
like {\tt graphicx}, it is possible to make a picture with a graphics
program, save it in {\tt .png} format (``portable network graphics'')
and have it appear in your document.  (The {\tt .jpg} format works, too,
but the images seem ``smudged''.)

\centerline{\includegraphics[scale=.7]{notes18a.png}}

\centerline{\includegraphics[scale=1.2]{notes18a.png}}

\centerline{\includegraphics[scale=1.2]{notes18a.jpg}}

(2) After you have first typed the {\tt .tex} file and try to run it
through \LaTeX, you certainly will have made errors.  In Texmaker, the
lower window will just say ``exited with errors'', and you will need to
click on the little ``screen'' icon next to this message to read the log 
file and find the errors.  If you issued the ``pdflatex'' command in a 
DOS window, the 
program will tell you where and what it {\it thinks} the first error is 
and say, with a question mark, ``Now what?''  Reply with an x (and a 
carriage return) to get back to the command prompt so that you can look
at the .log file.  In either case, when you have decided what went 
wrong, you can edit the {\tt .tex} file.

(3) After creating the {\tt .tex} file and viewing it, you will undoubtedly
want to make changes.  You can edit and resave and re``\TeX''the file as 
much as you want. If you are using Texmaker, the .pdf viewer will close 
the file automatically when you click the ``pdflatex'' arrow again.  But if 
you issued the ``pdflatex'' command through a DOS
window, before you run it through \LaTeX\ again, \underbar{close it} in the
viewer (Adobe Reader, or whatever).  Otherwise, \LaTeX\ will complain that
it can't write to the {\tt .pdf} file because it is in use by another
program.  Then you will have to close it and type {\tt firstfile.pdf}
again.  (Repeating commands in the command window is easy with the up and down
arrow keys.)

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\centerline{\includegraphics[scale=]{.png}}