i have to write a three page essay on the history of the trombone for my music theory class. just seeing if anyone had a good sorce.

Oh come now. IF you've got the time to post this request here and wait for an answer you most surely have the time to search the net.

Step one:
Get out your Grove's. The paper one that you read at night before goign to bed; or by candle light when there is no electricity to operate your computer.

Step two:
Go to the home page of the players in the major symphonies.

Step three:
http://www.trombone.org/articles/library/viewarticles.asp?ArtID=254

http://www.yeodoug.com/resources/text/history.html

http://home.att.net/~bobbeecher/trombone/trombone.html

well like douglas Yeo said in the source you sent me there is a great deal of information out there but it's hard to distinguish between what is real and what is fake.

I don't remember the title, but when I was working on my high school final project I read a book by Israeli trombonist Benny Sluchin on the history of the trombone. Maybe you could look for it. It might have been in french though, I read books in both french and english for that project and I'm really not sure what language it was in...

Go to your local msic store and just look at the inside of a beginner's trombone method book. Standard of Exellence has a good basic history on the trombone.
Or, if you don't want to go anywhere, search on wikipedia or something. That's not as a reliable source for accurate info, but it works.