Plane and spherical trigonometry :
Kells, Lyman Morse
Plane and spherical trigonometry : 2nd ed. / L.M. Kells ; Willis F. Kern ; James R. Bland. - New York ; London : McGraw-Hill, 1940.
Plane and spherical trigonometry : 2nd ed. / L.M. Kells ; Willis F. Kern ; James R. Bland. - New York ; London : McGraw-Hill, 1940.