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- Defination of Complex Number - Real part and imaginary part
- Need for Complex Numbers

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Complex Number is a combination of a real and an imaginary number in the form a + bi. a and b are real numbers, and. i is the "unit imaginary number" `sqrt(−1).`

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 z1 = a + ib and z2 = c + id are equal if a = c and b = d.