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In order that a triangle be strong it is necessary to inscribe supports at the three weak points.
A circular support is the most complete, and the only way in which the three smaller triangles remain ‘equal’ in size.

As the circle distorts so do the equality of the triangles lessen. Pressure applied at the weak point will distort the circle and cause stress.

Worth study is the question of where vulnerability is most likely: clearly between points. There are three points of the triangle and three points of primary vulnerability.
Struts can only reasonably operate from these three structural points.
A circle within the triangle is perhaps the strongest formula. It is also the simplest way to support the structure at exactly the points of vulnerability.
A direct connection is made between the three weakest points of the structure.

It is interesting that sub-structuring the triangle with an M shaped support exactly doubles the number of triangles. Or rather: two sets of small triangles. One set of large triangles. One large triangle } 7