Step-by-step explanation:
x² + 9 doesn't factor into (x − 3) (x + 3). That's the factorization for the difference of squares, not a sum of squares.
x² + 9 has only imaginary factors: (x − 3i) (x + 3i).
x = {-3i, 0, 3i}
If x is only real numbers, then x = {0}
