Square-Bracing Problem/Crossing Rods

Classic Problem

Let there be an unlimited supply of rigid rods of unit length which may be joined together at their ends with a hinged joint.

Let $4$ of these rods be used to construct a square.

How many more of these rods are needed to make the square rigid?

Rods are allowed to cross.

Solution

This solution uses $15$ rods:

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Sources

• Weisstein, Eric W. "Braced Polygon." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/BracedPolygon.html