Osculating Circle of the Conchoid of Nicomedes

r = a + sec t

References: J. Dennis Lawrence, A Catalog of Special Plane Curves, pp. 137-138.
                      蔣聲, 形形色色的曲線, pp. 99-101.
                      E. H. Lockwood, A Book of Curves, pp. 127-129.
                      R.C. Yates, Curves and Their Properties, pp. 31-33.