No fifth point is possible, and many topics do not have this fifth point;

But sometimes there may be errors, such as:

A(- 1，0)，B( 1，0)

The trajectory of point P of PA⊥PB is a whole circle according to the general steps of finding the trajectory, but actually y≠0.

Article 5 comes into play at this time; It plays a great role, because the point whose coordinate is the solution of the equation is not on the curve;