Let be the orthocentre and the circumcentre of a triangle with the length of side equal to . Cevians are constructed from vertices and so as to be tangent to , the circle passing through and and congruent to the circle centred at touching .
Let the cevians through and touch the circle at and respectively. If and are of integer lengths, what is their sum?
Aside: On the query of some, this is indeed an original problem of mine!
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It will be recalled that the length A H is twice the perpendicular distance of O from B C . This elementary result can be proved by the similiarity of triangles A H G and D O G noting the Euler line and that the median is split in a 2 : 1 ratio by G . (Here, G is the centroid and D the midpoint of B C .)
Suppose K , L , M be the feet of altitudes from A , B , C respectively. So, the circle γ has A H for diameter. This implies that it is the circle circumscribing the quadrilateral A L H M , because A H subtends a right angle at the point of intersection of γ and A C ( other than A ) and that makes it coincident with L . A similiar argument for M .
Now use the secant theorem as:
B M × B A = B T 2
But by the cyclic quadrilateral M A C K , again the secant theorem yields: B M × B A = B K × B C
We conclude: B T 2 = B K × B C
By a similiar argument: C U 2 = C K × C B
An intuitively obvious addition step yields: B T 2 + C U 2 = B C 2 = 2 0 1 4 2
Now then, B T − C U − 2 0 1 4 form a pythagorean triplet with 2 0 1 4 as the largest member. A simple way to work out the B T and C U is to factorize 2 0 1 4 and hunt a triplet with a factor as the largest in the triplet viz. hunting for x − y − 1 9 or x − y − 2 or x − y − 5 3 . The latter works : 2 8 − 4 5 − 5 3 . Magnify by 3 8 to 1 0 6 4 − 1 7 1 0 − 2 0 1 4 .
It so happens that this is the only triplet.(Why?)
The answer : 1 0 6 4 + 1 7 1 0 = 2 7 7 4 .
Hope, that was exhaustive. And error free!