Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
(a) The research circle used to extract the third corner through the first tangent; (b) the third and the fourth corners extracted using the first tangent. A tangent is traced through each of these new corners for extracting new ones in the two directions: bottom and up.
