I'm thinking of a scalene triangle in which one side is length 6. If both the barycenter and orthocenter lie on the triangle's incircle, what is the maximum distance between the barycenter and orthocenter? If this distance is , submit rounded to the nearest integer.
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This is done by number-crunching. I shall use the u v w -representation of a triangle. Any triangle has sides of the form a = v + w , b = u + w , c = u + v for u , v > 0 . The semiperimeter, area, inradius and circumradius of the triangle A B C can be written in terms of u , v , w as follows: s r = = u + v + w u + v + w u v w Δ R = = u v w ( u + v + w ) 4 Δ a b c = 4 u v w ( u + v + w ) ( u + v ) ( u + w ) ( v + w ) and we know that the distances between the orthocentre H , the incentre I and the centroid G are given by I H I G G H = 2 r 2 + 4 R 2 − 2 1 ( a 2 + b 2 + c 2 ) = 2 r 2 + 4 R 2 − ( u 2 + v 2 + w 2 + u v + u w + v w ) = 3 1 5 r 2 − 1 6 r R + s 2 = 3 2 9 R 2 − ( a 2 + b 2 + c 2 ) = 3 2 9 R 2 − 2 ( u 2 + v 2 + w 2 + u v + u w + v w ) We want to solve the equations I G = I H = r v + w = 6 over the range u > 0 and 0 < v < 6 . For definiteness, we assume that v ≤ w , and so we solve over u > 0 and 0 < v ≤ 3 . Solving these equations numerically yields three possible solutions: ( u , v , w ) = ( 1 . 0 4 2 1 3 9 9 1 7 4 8 1 0 9 8 8 , 1 . 3 1 0 3 5 3 3 3 5 5 9 3 0 8 3 , 4 . 6 8 9 6 4 6 6 6 4 4 0 6 9 1 7 ) ( 1 . 3 7 1 6 7 0 0 5 4 5 6 9 4 0 3 2 , 1 . 0 9 0 9 0 5 8 4 8 5 6 1 2 6 , 4 . 9 0 9 0 9 4 1 5 1 4 3 8 7 4 ) ( 1 1 . 9 6 0 8 7 5 9 5 5 6 1 4 9 9 7 , 2 . 6 5 7 9 6 2 7 7 9 1 5 5 9 0 9 5 , 3 . 3 4 2 0 3 7 2 2 0 8 4 4 0 9 0 5 ) which give the following values of G H : 1 . 7 9 5 3 4 2 6 0 7 4 8 1 4 3 2 3 1 . 8 7 9 3 5 3 9 3 1 0 9 8 4 5 0 8 4 . 5 7 8 9 9 5 3 4 0 7 1 4 3 5 6 respectively. This makes the last solution of the three the one we want. The desired triangle has sides a = 6 , b = 1 5 . 3 0 2 9 1 3 1 7 6 4 5 9 0 8 8 and c = 1 4 . 6 1 8 8 3 8 7 3 4 7 7 0 9 0 6 , and d = G H = 4 . 5 7 8 9 9 5 3 4 0 7 1 4 3 5 6 , so that 1 0 4 d = 4 5 7 8 9 . 9 5 3 4 0 7 1 4 3 5 6 , which rounds to 4 5 7 9 0 .