Final answer:
The nonpermissible replacement for x in the given quadratic equation is any value that would make the equation undefined.
Step-by-step explanation:
The expression x² - 4x - 8 represents a quadratic equation. In a quadratic equation, the nonpermissible replacement for x is any value that would make the equation undefined. Since this is a simple quadratic equation with no denominators or square roots, there are no nonpermissible replacements for x. You can substitute any real number for x in this expression and find a valid result.
Learn more about Nonpermissible replacements in quadratic equations