Locus pocus

The blue vertex is fixed in the plane. The green vertex can be anywhere on a circle. The yellow vertex completes an equilateral triangle. What is the locus of the yellow vertex?

Scroll down for a solution to this problem.


The locus is a congruent circle.

Solution by Stéphane Bernard.

The locus is a circle of same radius centered on the top vertex of the equilateral built from segment AO. It’s a vector thing : r vector= green vector – blue vector.


Please find here the video solution: Video: Locus pocus.

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