**François Rideau** proposed another problem : *the construction of the
tangent to the quartic at point T* .

This problem is difficult from the mathematical point of view and the confirmation
with Cabri is amazing.

Here is the **François Rideau**'s figure:

**Other loci can be constructed thanks to F. Rideau's figure**. The pedal of the
nephroïd is a rosace:

**The pedal of the quartic is a non-regular quadrifolium** (four-leafed rose):