HERON IAN INDETERMINATE EQUATIONS 447
and b. The method employed is to take the sum of the area
and the perimeter S + 2 s, separated into its two obvious
factors s(r+2), to put s(r+2) = A (the given number), and-
tlien to separate A into suitable factors to which s and r + 2
may be equated. They must obviously be such that sr, the
area, is divisible by 6. To take the first example where
A — 280 : the possible factors are 2 x 140, 4 x 70, 5 x 56, 7 x 40,
8 x 35, 10 x 28, 14 x 20. The suitable factors in this case are
r + 2 = 8, s = 35, because r is then equal to 6, and rs is
a multiple of 6.
The author then says that
a = i [6 + 35- V{ (6 + 35) 2 -8.6.35}] = £(41- 11 = 20,
6 = i(41 + l)= 21,
c = 35-6 = 29.
The triangle is therefore (20, 21, 29) in this case. The
triangles found in the other three cases, by the same method,
are (9, 40, 41), (8, 15, 17) and (9, 12, 15).
Unfortunately there is no guide to the date of the problems
just given. The probability is that the original formulation
of the most important of the problems belongs to the period
between Euclid and Diophantus. This supposition best agrees
with the fact that the problems include nothing taken from
the great collection in the Arithmetica. On the other hand,
it is strange that none of the seven problems above mentioned
is found in Diophantus. The five relating to rational right-
angled triangles might well have been included by him ; thus
he finds rational right-angled triangles such that the area plus
or minus one of the perpendiculars is a given number, but not
the rational triangle which has a given area; and he finds
rational right-angled triangles such that the area plus or minus
the sum of two sides is a given number, but not the rational
triangle such that the sum of the area and the three sides is
a given number. The omitted problems might, it is true, have
come in the lost Books ; but, on the other hand, Book YI would
have been the appropriate place for them.
The crowning example of a difficult indeterminate problem
propounded before Diophantus’s time is the Cattle-Problem
attributed to Archimedes, described above (pp. 97-8).
