Giovanni Domenico Cassini was born on June 8, 1625. He investigated the curves that are now known as the Cassini ovals defined by equations of the form

where

*q*

_{1 }and

*q*

_{2}are fixed points, "dist" is the Euclidean distance in the plane, and b is a constant. The above picture displays a few Cassini ovals, with foci

*q*

_{1}(-1, 0) and

*q*

_{2}(1, 0), annotated with the value of

*b*

^{2}.

In 1680, while director of the Paris Observatory he discovered the identity

satisfied by the Fibonacci numbers. This is now known as the Cassini identity. A quick proof by using determinants:

A bijective proof was provided by M. Werman and D. Zeilberger - "A bijective proof of Cassini's Fibonacci identity", Discrete Mathematics 58 (1), 109 (1986).

Also see the Cassini biography from MacTutor.