Concept

Complex Conjugate

The complex conjugate of a complex number has the same real part, but the imaginary part is the opposite of its original sign. Therefore, changing the sign of the imaginary part of a complex number creates its complex conjugate. It is denoted by a line drawn above the complex number.

a+bi = a-bi or a-bi = a+bi

For example, the complex conjugate of z = 3 - 5i is z= 3 + 5i. It is worth noting that the product of a complex number and its conjugate is a real number.

z* z
Substitute a+bi for z and simplify
( a+bi)(a+bi)
(a+bi)( a-bi)
a^2-abi+abi-b^2i^2
a^2-b^2i^2
a^2-b^2(-1)
a^2+b^2

This fact is very useful when simplifying quotients whose denominators are complex numbers.

Exercises
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