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z^2-i=0 equation

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Numerical solution:

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The solution

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 2        
z  - I = 0
$$z^{2} - i = 0$$
Detail solution
This equation is of the form
a*z^2 + b*z + c = 0

A quadratic equation can be solved
using the discriminant.
The roots of the quadratic equation:
$$z_{1} = \frac{\sqrt{D} - b}{2 a}$$
$$z_{2} = \frac{- \sqrt{D} - b}{2 a}$$
where D = b^2 - 4*a*c - it is the discriminant.
Because
$$a = 1$$
$$b = 0$$
$$c = - i$$
, then
D = b^2 - 4 * a * c = 

(0)^2 - 4 * (1) * (-i) = 4*i

The equation has two roots.
z1 = (-b + sqrt(D)) / (2*a)

z2 = (-b - sqrt(D)) / (2*a)

or
$$z_{1} = \sqrt{i}$$
$$z_{2} = - \sqrt{i}$$
Vieta's Theorem
it is reduced quadratic equation
$$p z + q + z^{2} = 0$$
where
$$p = \frac{b}{a}$$
$$p = 0$$
$$q = \frac{c}{a}$$
$$q = - i$$
Vieta Formulas
$$z_{1} + z_{2} = - p$$
$$z_{1} z_{2} = q$$
$$z_{1} + z_{2} = 0$$
$$z_{1} z_{2} = - i$$
The graph
Rapid solution [src]
         ___       ___
       \/ 2    I*\/ 2 
z1 = - ----- - -------
         2        2   
$$z_{1} = - \frac{\sqrt{2}}{2} - \frac{\sqrt{2} i}{2}$$
       ___       ___
     \/ 2    I*\/ 2 
z2 = ----- + -------
       2        2   
$$z_{2} = \frac{\sqrt{2}}{2} + \frac{\sqrt{2} i}{2}$$
z2 = sqrt(2)/2 + sqrt(2)*i/2
Sum and product of roots [src]
sum
    ___       ___     ___       ___
  \/ 2    I*\/ 2    \/ 2    I*\/ 2 
- ----- - ------- + ----- + -------
    2        2        2        2   
$$\left(- \frac{\sqrt{2}}{2} - \frac{\sqrt{2} i}{2}\right) + \left(\frac{\sqrt{2}}{2} + \frac{\sqrt{2} i}{2}\right)$$
=
0
$$0$$
product
/    ___       ___\ /  ___       ___\
|  \/ 2    I*\/ 2 | |\/ 2    I*\/ 2 |
|- ----- - -------|*|----- + -------|
\    2        2   / \  2        2   /
$$\left(- \frac{\sqrt{2}}{2} - \frac{\sqrt{2} i}{2}\right) \left(\frac{\sqrt{2}}{2} + \frac{\sqrt{2} i}{2}\right)$$
=
-I
$$- i$$
-i
Numerical answer [src]
z1 = -0.707106781186548 - 0.707106781186548*i
z2 = 0.707106781186548 + 0.707106781186548*i
z2 = 0.707106781186548 + 0.707106781186548*i