Double Mean Proportionals

Hipprocrate of Chios, a famous Greek mathematician did a lot of influential work on the three classical problems.  He considered Delian problem in a more general form - the problem of constructing the so-called "double mean proportionals":  Given two lengths and , find the lengths and such that

By simple algebra, it is easy to see that if and , then

How Hipprocrate came up with such idea?  One possible explanation is that he was inspired by the following well-known result at his time: The following two problems are equivalent:
  • Given a square, construct a square whose ratio between their areas equals a given ratio .
  • Given and , construct the "mean proportional" between them i.e. a number such that .
It is easy to prove this by modern algebra.  For simplicity, suppose is the length of the side of the given square.  Then we have

That is to say, is the length of the side of the required square.