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Double tiling congruent triangles with little else in common

Puzzling Asked on February 22, 2021

When you really want to tile more than one layer
but triple tiling is just too much of a good thing,
surely the happy medium is double tiling.

  • How may a mosaic of more than 900 sections be double tiled
    with congruent triangles along the 6 guidelines listed below?

Here are two examples of double tiling with congruent triangles.
The first example demonstrates most guidelines of this puzzle
while the second follows the toughest guidelines as well.

In the first example, eight overlapping
26.6°- 63.4°- 90°
triangles double tile a square mosaic of
15 sections where:

  1. “Double tiling” is taken to mean that
    every section of a mosaic is completely covered
    by portions of exactly two tiles
    and that all tiles lay completely within that mosaic.

  2. The tiles are
    congruent
    triangles.

  3. Each tile is uniquely oriented.

  4. The mosaic is edge-contiguous in that all sections may be
    visited along a single unbroken path that stays within the mosaic
    while crossing tile edges from section to section
    without touching any vertex.

In the second example, four overlapping congruent
30°- 60°- 90°
triangles double tile a triangular mosaic of
4 sections where, moreover:

  1. Every angle is a whole number of degrees.

  2. No distinct lines are parallel.
    (Parallel tile edges may, however, lie along a single continuous line.)

Bounty challenges, achievability unknown

  • Double tile a mosaic other than the second example above
    that follows all 6 guidelines and has no holes.

  • Double tile a mosaic that follows all 6 guidelines
    and whose outline is not
    bilaterally symmetric.

(All interesting double tilings,
including those with fewer than 901 sections
and/or those that disregard some of the above guidelines,
deserve votes of approval.)

2 Answers

I have a hunch the intended solution may be something like

For better clarity here are a few smaller examples:

Correct answer by Paul Panzer on February 22, 2021

(Community wiki – feel free to add or edit.)

In lieu of hints from puzzle’s poser here are a couple of almost-solutions that follow most guidelines but not all. Ten congruent 36°- 72°- 72° triangles double tile a contiguous mosaic of 10 sections but the triangles are not uniquely oriented and the mosaic has 5 pairs of parallel lines:

Twelve uniquely oriented congruent 30°- 60°- 90° triangles double tile a contiguous 12-section mosaic that yet includes 6 pairs of parallel lines:

Answered by humn on February 22, 2021

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