how was Willy Loman a tragic figure in the play?

First of all, make sure you are clear on what a tragic figure is:
http://www.answers.com/tragic

Then be sure to read the character analyses at these sites:

http://www.sparknotes.com/lit
and
http://www.gradesaver.com/classicnotes/titles

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go to pinkmonkey and you will find characther of Willy that is an excellent website!

Yes, PinkMonkey is a well-known website with comprehensive character analyses. You can find information on Willy Loman's tragic nature by searching for the character analysis of Willy Loman on the PinkMonkey website. The character analysis will provide you with insights into Willy's personality, actions, and his ultimate downfall, which contributes to his status as a tragic figure in the play.