is a triangle with integral sides. is the midpoint of . The in-circle with centre touches and at and respectively and is the projection of on . Suppose that is a parallelogram and . Find .
, 1997
Solution
The product is .
Let , , , , be the lengths of , , , the inradius and the semiperimeter of respectively. Let be the midpoint of , and let be the intersection point of and . It is well-known that . Therefore, we have . (Alternatively, one can prove this by noting and .)

Note that by the midpoint theorem. Since is a parallelogram, we have
On the other hand, we have
Equating these, we obtain . As it is given that , this yields . Then the given condition becomes . This can be factorized as
As and are larger than , we must have and up to permutation. This gives or . Therefore, .
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