Gemma Frisius's Arithmeticae Methodus Facilis

This is the title page of the Arithmeticae Practicae Methodus Facilis (1540), by Gemma Frisius (originally Regnier Gemma) (1508-1555).  Gemma Frisius was best known for his work in astronomy and map-making; he worked closely with Gerardus Mercator in making an early globe.  He also suggested a method for determining longitude at sea.

On this page is an example of the use of double false position to solve a problem in two unknowns.

Here, Gemma describes a method of finding square roots.