This demo includes a single graphical window that displays a curve
X(t) (which you may change in the appropriate textbox in the control
window), a point C that you may change by clicking and dragging it, the
point X(t_{0}), the segment of the tangent line to the curve
X(t) at X(t_{0})
connecting X(t_{0}) to the closest point (shown in red) on the
tangent
line to C, the line segment connecting the red point to C, which is
perpendicular to the tangent line, and the pedal curve traced out by
the red point as t_{0} runs from its minimum to its maximum
value.

Change the value of t_{0} and other variables as in earlier demos.

As in earlier demos there is the "Show Color Spectrum" option.
In this demo it colors everything except X(t0).