An X-ray of a chambered nautilus shell shows similar properties to the logarithmic spiral which is a graph of a solution of the differential equation dr/dθ=br. (X-ray courtesy of C. C. Jones, Union College, Schenectady, NY. "Logarithmic Spiral" courtesy of Eric W. Weisstein, from MathWorld - A Wolfram Web Resource
This course covers the same material as Differential Equations (18.03) with more emphasis on theory. In addition, it treats mathematical aspects of ordinary differential equations such as existence theorems.