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“What are the chances that three points chosen at random would line up?” That was the question that came to mind as I contemplated the arc created by rotating the triangle’s base, and how precisely it fits the painting.

With the arc tangent to the pediment, its construction unfolded with ease.

📐 By placing our imaginary compass on M this time, the rotation of the triangle’s base gives us a mirror image of the arc traced in the previous post. Together, these arcs outline the familiar silhouette of a Gothic arch around the triangle.

Since this arch touches the semi-circular pediment at a tangent, it follows that a circle must have been used to draw its outer edge.

So the question is: what is the radius of that circle?

💡 The first intuition is the correct one: the pediment is defined by a circle of radius 1 (one module of the grid = 1).