 or $z_1 = (x(b), y(b))$ is its <em>terminal point</em>.
                    The expression $z(t) = x(t) + iy(t)$ could also be
                    interpreted as a two-dimensional vector function.
                    Consequently, $z(a)$ and $z(b)$ can be interpreted as position
                    vectors. As $t$ varies from $t = a$ to $t = b$ we can envision the curve $C$
                    being traced out by the moving arrowhead of $z(t).$
                    This can be appreciated in the following a