In this lecture Prof Susskind discusses the Mathematics of spheres. He discusses a 1-sphere (circle), a 2-sphere (surface of the earth), and a 3-sphere. Prof Susskind discusses how n-spheres can be defined by n parameters. He presents special geometries that have constant curvature. Prof Susskind discusses the general concept of curvature and cosmology of a spherical universe. He further discusses the possibility of negative curvature, and the cosmology of a negative curved universe. We discuss the connection of the equations of cosmology and the general theory of relatively. Prof Susskind discusses the Newtonian point of view and Einsteinian point of view regarding escape velocity for universe expansion.