3. Negative of a Point, Subtraction, Conjugate

As in other number systems, if P + N = O, one writes N = -P and calls N the negative of P. It follows from the definition of addition of points in the Argand Plane that N is the point such that the directed line segment has the same magnitude and direction as i.e., N is the point such that O is the midpoint of segment PN. If then clearly

See Figure 4.

Figure 4

The difference E - F is the point G such that E = F + G. One can also obtain the difference G = E - F using the formula
G = E + (-F). See Figure 5.

Figure 5

Figure 6

In the Argand Plane, the conjugate of a point is the point with the same absolute value as P but with the argument the negative of that of P. Note that a point P and its conjugate are symmetrically situated with respect to the straight line determined by O and U. See Figure 6.