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MathNet 1999 — Part 01 Question 55

Math Olympiad Vault · MathNet 1999 — Part 01

Question 55

Given a triangle $ABC$, with centroid $G$.

a) Proof that for any point on the $M$ plane the following is true:
$$
\overline{MA}^{2}+\overline{MB}^{2}+\overline{MC}^{2} \geq \overline{GA}^{2}+\overline{GB}^{2}+\overline{GC}^{2}
$$
obtaining equality if and only if $M=G$.

b) Given a number $k\gt \overline{GA}^{2}+\overline{GB}^{2}+\overline{GC}^{2}$, find the locus of the points $M$ such that
$$
\overline{MA}^{2}+\overline{MB}^{2}+\overline{MC}^{2}=k
$$