Complex Number and Quadratic Equations  Solutions and Study Material
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Complex Number : Let us denote by the symbol i. Then ,we have = 1. This means that I is a solution of the equation
A number of the form a + ib, where a and b are real numbers, is defined to be a complex .
Complex Number: 2 + 3i, , are complex numbers.
For the Complex Number z = a + ib, a is called the real part, denoted by Re z and b is called the imaginary part denoted by Im z of the complex number z. For example, if z = 2 + i5, then Re z = 2 and Im z = 5.
Two complex numbers = a + ib and = c + id are equal if a = c and b = d
Example: If 4x + i(3x – y) = 3 + i (– 6), where x and y are real numbers, then find the values of x and y.
Solution: We have , 4x + i (3x – y) = 3 + i (–6) ... (1)
Equating the real and the imaginary parts of (1), we get ,4x = 3, 3x – y = – 6,
which, on solving simultaneously, give x = , y =
Algebra of Complex Numbers: In this Section, we shall develop the algebra of complex numbers
Addition of two complex numbers Let = a + ib and = c + id be any two complex numbers .Then , the is define as follows :
= (a + c) + i(b + d) , which is again a complex number.
For Example (2 + 3i) +(6 +5i) = (26) + I (3 + 5) = (4 + 8 i)
The addition of complex number satisfy the following properties:
 The closure law The sum of two complex numbers is a complex number, i.e., is a complex number for all complex numbers Let and Let
 The commutative law For any two complex numbers and ,
 The associative law For any three complex numbers ,
 The existence of additive identity There exists the complex number 0 + i 0 (denoted as 0), called the additive identity or the zero complex number, such that, for every complex number z, z + 0 = z
 The existence of additive inverse To every complex number z = a + ib, we have the complex number – a + i(– b) (denoted as – z), called the additive inverse or negative of z. We observe that z + (–z) = 0 (the additive identity)
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