For many applications we find that it is much easier to represent our physical quantities in terms of complex numbers rather than just using real numbers alone. The concept of complex numbers comes from the continuation of functions such as square-root and logarithm that only apply to positive numbers in their traditional definitions. Figure 1 shows the function √ x. Other functions like ln x, sinx, etc., also have limits on their arguments, and complex numbers allow us to define these functions over the full range of real numbers.