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825.11
They then used a straightedge to connect points C
and C' with a line that
they said bisected line AB perpendicularly, being generated
by equidistance from either
point on either side. Thus the Greeks arrived at their
right triangle; in fact, their four right
triangles. We will designate as point D the intersection
of the lines CC' and AB. This gave
the Greeks four angles around a common point. The four
right triangles ADC, BDC,
ADC', and BDC' have hypotenuses and legs that are, as
is apparent from even the most
casual inspection, of three different lengths. The leg
DB, for instance, is by equidistance
construction exactly one-half of AB, since AB was the
radius of the two original circles
whose circumferences ran through one another's centers.
By divider inspections, DB is
less than CD and CD is less than CB. The length of the
line CD is unknown in respect to
the original lines AB, BD, or AC, lines that represented
the original opening of the
dividers. They have established, however, with satisfaction
of the rules of their game, that
360 degrees of circular unity at D could be divided
into four equal 90-degree angles
entirely and evenly surrounding point D.
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