Mr. Giuseppe Cammarata at the Liceo Scientifico Statale Benedetto Croce in Palermo, Italy is using this material in his Course IV F. Many of the solutions below were written by his students.

17. From the definition of the sum of two points in the Argand plane, we have that the parallelogram obtained in this case collapses into a line segment, since P + N = O where O is the origin of the plane. Then and are in the same straight line but they have opposite directions; it follows that the point N has magnitude r = 6 and argument Then the polar form of N is:

Solution by Laura Marretta and Candido Zacchino
Liceo Scientifico Statale Benedetto Croce, April 2001.