There is some discussion of Eudoxus' theory
of ratios in the pages
The first author doesn't seem to have read
Book V, where the basic theory is laid out.
The second doesn't seem to have read
Book VI, where it is applied (and where the proof
of Pythagoras' Theorem he admires is in fact to be found).
To give you an idea of how subtle the theory is,
the opening Theorem of Book VI is that
if you are given two rectangles with the same
height, the ratio of their areas is the same as the ratio
of their bases.
If you try
to prove this yourself from
elementary principles, you will
understand immediately what difficulty
the Greeks faced, and admire them enormously
for getting around it.
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