# Geometry, Training

let $D, E, F$ be midpoints of $BC, CA, AB$. Let $(d)$ be any line and let $AA_1, DD_1, EE_1, FF_1$ be distances from $A, D, E, F$ to the line $(d)$.

Prove that  $\overline{AA_1}=\overline{DD_1}+\overline{EE_1}+\overline{FF_1}$

Author: Van Khea, Prey Veng, Cambodia