Who was the black man that momorized the blueprints for Washington DC after the frenchman who was orginally building it quit?

That's been credited to Benjamin Banneker, but it may not be true of him or anyone else. Check this article.

http://en.wikipedia.org/wiki/Benjamin_Banneker

The person you are referring to is Benjamin Banneker. He was an African American mathematician, astronomer, and surveyor who played a significant role in the early development of Washington, D.C. It is important to note that Benjamin Banneker did not "memorize" the blueprints for Washington, D.C., but rather he provided surveying and calculations to help establish the layout of the city.

To find the answer to this question, you can follow these steps:

1. Start by searching for information about the construction of Washington, D.C. You can use a search engine like Google to do so.

2. Look for information about individuals involved in the planning and construction of Washington, D.C. Pay attention to any notable figures who contributed to the project.

3. Identify the Frenchman who initially worked on the city. Pierre Charles L'Enfant was the French architect and engineer who created the initial plan for Washington, D.C.

4. Look for information about any individuals, particularly African Americans, who played a role in the development of the city after L'Enfant's departure. Benjamin Banneker's contributions should come up during your search.

5. Read articles, biographies, or historical accounts that provide more details about Benjamin Banneker's involvement in the construction of Washington, D.C. These sources will provide you with a comprehensive understanding of his contributions and the role he played in preserving and continuing L'Enfant's plans.

By following these steps, you can verify the information about Benjamin Banneker's involvement in the construction of Washington, D.C.