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MathNet 2015-part-05 — 191 problems (EN–VI) Question 38

Math Olympiad Vault · MathNet 2015-part-05 — 191 problems (EN–VI)

Question 38

The points $T, A, B, C$ are non-coplanar and the straight lines $a, b, c$ are the parallels from the centroid $G$ of the triangle $ABC$ to the straight lines $TA, TB$, respectively $TC$. Let $\{A'\} = a \cap (TBC)$, $\{B'\} = b \cap (TAC)$ and $\{C'\} = c \cap (TAB)$.

a) Prove that $(A'B'C') \parallel (ABC)$.

b) Compute the distance between the planes $(A'B'C')$ and $(ABC)$ as a function of the distance $a$ from $T$ to the plane $(ABC)$.