The first page of Pathway to Knowledge by Robert Recorde (1510-1558). A version of Euclid's Elements, with commentary by Recorde to make it easier to understand. This page includes Euclid's first three postulates.
The cost per hour of running a certain steamboat is proportional to the cube of its velocity in still water. At what speed should it be run to make a trip up stream against a four-mile current most economically?