Publisher Summary This chapter discusses complex numbers. A number of the form a + ib, where a and b are real numbers, is called a complex number. Real numbers can be regarded as complex numbers for which b is zero. Thus, there is need only to consider complex numbers because real numbers will be contained within the system of complex numbers. This will require to consider carefully the rules for the addition and multiplication of complex numbers so that these rules, when applied to real numbers of the form (a + i0), give the correct results within the real number system. The chapter highlights the rules governing the addition, subtraction, multiplication, and division of complex numbers. These rules are defined so that they become the rules of algebra for real numbers when applied to complex numbers of the form a + i0. The chapter defines what is meant by the equality of two complex numbers a + ib and c + id, where a, b, c, and d are real numbers. It also shows the geometrical representation of complex numbers. This representation of complex numbers enables to give a geometrical interpretation of the rules for the addition and multiplication of complex numbers.