Question

X^2+6x+90=0
A)x=-3+9i, -3-9i
B)x=-12
C)x=6,-12
D)x=-3+9i

Answer 1

First, we con solve the quadratic by completing the squares
x^2 + 6x + 90 = 0
x^2 + 6x = -90
x^2 + 6x + 9 = -81 (to complete the square, half teh b calue squared gives us the c value)
(x + 3)^2 = -81
x +3 = +√(-81) and -√-81
x + 3= 9i and -9i
x = -3 + 9i and -3 - 9i
Choice A is correct