Wallace-Simson lines
If P is any point belonging to a circle circunscribed to a triangle then the three points obtained by orthogonally projecting P on the three sides of the triangle are collinear. Wallace was the first to discover this but the line obtained is called the Wallace-Simson line of P.
We can change the triangle moving its vertices. We control the point P using the buttons or dragging the point using the mouse.
This is consecuence of a circle property (Euclides, III.21 or III.22) that saids that the oposite angles of every cuadrangle inscribed in a circle are together equal to two right angles (or equal).
We can see a "Mostration" about Wallace line.
REFERENCES
Coxeter - Introduction to Geometry (John Wiley and sons).
