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Imaginary Number : The square root of a negative real number is called Imaginary Number. The Unit of imaginary number is denoted by i=√(-1). As for example, √(-9)=3i.

Complex Number : The Complex Number is defined by a+ib where a and b are real numbers and i=√(-1). As for example, 3+5i is a Complex Number.

Conjugate Complex Number : If z=x+iy be a Complex Number, then z=x-iy is called the Conjugate Complex Number of complex number z. It is denoted by z=x-iy. As for example, If z=5+4i, then z=5-4i and If z=-3-6i, then z=-3+6i.

Modulas : If z=x+iy be a Complex Number and x=rcosθ, y=rsinθ, then r=|z|=√(x^{2}+y^{2}) is called the modulas of z. As for example, If z=3+4i, then Modulas |z|=√(3^{2}+4^{2})=5.

Argument : If z=x+iy be a Complex Number and x=rcosθ, y=rsinθ, then θ=tan^{-1}(y/x) is called the Argument of z. As for example, If z=1+i, then Argument θ=tan^{-1}(1/1)=45^{0}.

Real part : If z=x+iy be a Complex Number, then x is called the Real part of complex number z. It is denoted by Re(z)=x. As for example, If z=7+4i, then Re(z)=7.

Imaginary part : If z=x+iy be a Complex Number, then x is called the Imaginary part of complex number z. It is denoted by Im(z)=y. As for example, If z=7+4i, then Im(z)=4.

Argand plane : The set C of complex numbers is naturally identified with the plane R^{2}. This plane is called the Argand plane. A complex number z = x+i y, its real and imaginary parts x and y define an element (x, y) of R^{2}.

Reciprocal of a Complex Number : The reciprocal of a complex number is a complex number which is calculating 1 divided by that complex number. For example, the reciprocal of a complex number 1+i is 1/(1+i)=(1-i)/{(1+i)(1-i)}=(1-i)/(1-i^{2})=(1-i)/{(1-(-1)}=(1-i)/2=1/2-i/2