The answer to your question is -2999.9HOPED I HELPED!
This one is so easy that your brain refuses to accept it.
It's looking for a harder answer, but can't find it !
You're totally correct, as far you went. x² + 2x does = -1
Now add ' 1 ' to each side: x² + 2x + 1 = 0
Can you factor that quadratic ?
Can you mash it through the quadratic formula ?
Actually, it's the simplest possible perfect square.
x² + 2x + 1 = (x + 1)²
So the solutions of x² + 2x + 1 = 0 are both x = -1 .
Don't say anything.
I know it's embarrassing.
We have:

Then we use trigonometric identities to change the negative sign of the trigonometric functions, so:

We clear f(x):

we simply what we can:

Thus, the correct answer is;
So to factor
factor out a x+z
(x+z)(x^2-xz+z^2)
the factors are
x+z and x^2-xz+z^2