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Austria 2014

Austria 2014 geometry

Problem

Consider a triangle . The midpoints of the sides , , and are denoted by , , and , respectively. Assume that the median is perpendicular to the median and that their lengths are given by and . Compute the length of the third median .
Solution
We denote the centroid of the triangle by . As the centroid divides each median into parts in the ratio , we have By the Pythagorean theorem in the triangle , we obtain

By Thales' theorem, lies on the circle with center and diameter . Therefore, we have As , we obtain
Final answer
45/2

Techniques

Triangle centers: centroid, incenter, circumcenter, orthocenter, Euler line, nine-point circleConstructions and loci