Answer:
z=i+2
,
z=i-2
Step-by-step explanation:
Remember that the quadratic equation [tex]az^2+bz+c=0[/tex] has the complex solutions [tex]z=\frac{-b\pm \sqrt{b^2-4ac}}{2a} [/tex] (this is the quadratic formula).
Apply this with a=1, b=-2i and c=-5 to get:
[tex]z=\frac{2i\pm \sqrt{(-2i)^2-4(-5)}}{2}=\frac{2i\pm \sqrt{-4+20}}{2}=\frac{2i\pm 4}{2} [/tex]. Then the solutions are
[tex]z_1=\frac{2i+4}{2}=i+2[/tex] and [tex]z_1=\frac{2i-4}{2}=i-2[/tex]
It isn't necessary to use De Moivre's formula.