Despite their ambiguous “imaginary” designation there is nothing imaginary about a complex number. In its geometrical interpretation, it is a 2D number associated with a point in a Cartesian plane where the horizontal axis is called “real” and the vertical axis “imaginary” (as measured in the units i or, in engineering sciences, j) thus forming the complex plane. Thus, the understanding of its formal relations to vectors and trigonometry, its algebraic forms and applications, Euler’s equation, and complex plane is the main objective of exercises in this chapter.