The equilateral triangle has reflection symmetry in 3 directions. This means you can place a mirror on the equilateral triangle in 3 different directions and the image will still look like an equilateral triangle. The equilateral triangle also has 3-fold rotational symmetry. This means you can rotate the equilateral triangle 120 degrees and it will always line up with itself. When viewed along a yellow strut, many symmetrical models built with Zometool will exhibit 3-fold symmetries like the equilateral triangle.
Yellow planes are perpendicular to yellow struts.
The 3-fold dodecahedron shadow cannot be built in the yellow plane using Zometool parts. Back to questions 3. The cross-section of the red strut is an equilateral pentagon. It has 5 equal sides and 5 corners. The equilateral pentagon has reflection symmetry in 5 directions.