Algebra of Complex Numbers

In this Section, we shall develop the algebra of complex numbers.

Addition of two complex numbers

Let $z_{1}=a+ib$ and $z_{2}=c+id$ be any two complex numbers.Then the sum $z_{1}+z_{2}$is defined as follows:

$z_{1}+z_{2}=(a+c)+i(b+d)$ which is also a complex number.

Example: Let $z_{1}=2+i3$ and $z_{2}=-6+i5$. Hence $z_{1}+z_{2}=(2-6)+i(3+5)=-4+i8$

The addition of complex numbers satisfy the following properties:

Closure law

The sum of two complex numbers is a complex number. $z_{1}+z_{2}$ is a complex number for all complex numbers $z_{1}$ and $z_{2}$.

Commutative law

For any two complex numbers $z_{1}$ and $z_{2}$, $z_{1}+z_{2}=z_{2}+z_{1}$

Associative law

For any three complex numbers $z_{1},z_{2},z_{3}$ , $(z_{1}+z_{2})+z_{3}=z_{1}+(z_{2}+z_{3})$

Existence of additive identity

There exists the complex number $0+i0$ (denoted as $0$) called the additive identity or the zero complex number, such that for every complex number $z$ ,$z+0=z$

Existence of additive inverse

To every complex number $z=a+ib$ , we have the complex number $-z=-a+i(-b)$ called the additive inverse or negative of $z$. We observe that $z+(-z)=0$ (the additive identity).