Answer:
x = 2 + 6i, x - 6i.
Step-by-step explanation:
To factor this you need 2 numbers whose product is + 40 and whose sum is -4. There are no such numbers so we could use the method of completing the square:
x^2 - 4x + 40 = 90
x^2 - 4x = -40
(x - 2)^2 - 4 = -40
(x - 2)^2 = -36 - So the roots are complex numbers:
x - 2 = +/-√36
x = 2 + 6i, x - 6i.
