Hello topsquark,
Thanks for your reply!
first: It wasn't me who "invented" this method.
second: The following method only works if:
 the coefficients are arranged(?) symmetrically in the equation
and

Then you can divide the equation by x²:
Divide by x²
Rearrange:
Factor:
Now set
. Then
. That means
And now you can use substitution. The equation becomes:
which will give z = 5 or z = 3.
Resubstituate to solve for x
The actual solution for x doesn't matter. I only wanted to show a very special method to solve those equations.
EB