Question

Can anyone please help me with this?

Answer 1

Using difference of squares

$a^{2} -b^{2}$ =(a-b)(a+b)

with a = x and b = 3$\sqrt{2}$i

$x^{2}$ + 18 =(x-3$\sqrt{2}$ i)(x+3$\sqrt{2}$ i)