Let's try to simplify x^2 + 16. It's a sum of two squares:
x^2 + 16 = 0
x^2 = -16
The problem is, we can't take a square root of a negative. This is where imaginary numbers come in.
Remember that square roots have a plus or minus symbol outside:
±√-16 = ±4i
Our two roots are 4i and -4i. Therefore, the trinomial simplifies to:
(x + 4i)(x - 4i)
If we attempt to divide x + 4 by these two binomials, we will find that 4 and 4i are not like terms. Therefore, we can't simplify this expression.