Joseph sent the following, and I printed it.

Livio Zucca -- Joseph DeVincentis solution is not the best!!! The best solution is with 6 triangles! The first solver of my puzzle was Paolo Licheri on an Italian News Group. Here below a little correspondence with Michael Reid. "hi, thanks for your interesting dissection puzzle; i found a solution with 6 pieces. i assume you didn't have fewer than that. mike"

Solvers were baiocchi, Jeffrey Gosselin, and

Joseph DeVincentis -- I wouldn't have thought it possible, but if you connect
all 6 vertices of the hexagon to a point (11-sqrt(21))/2 units from the left-most
vertex along the horizontal axis toward the opposite vertex, all 6 resulting
triangles are similar, in a ratio of approximately 3.209:4.005:5 as you go from
left to right on either side of the horizontal axis.