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By inversion at BC, ABC becomes an equiangular triangle A′BC.

It opens with a definition of a regular polygon as one that is both equilateral and equiangular.

In a given circle to inscribe a triangle equiangular to a given triangle; Prop.

The next kind of propositions we have to consider are general propositions, such as “all men are mortal,” “all equilateral triangles are equiangular.”

Let the Triangle aei be given: And the circle, o, into which a Triangle equiangular to the triangle given, is to be inscribed.