Final answer:
The expression x²-8 is not a difference of perfect squares because while x² is a perfect square, 8 is not the square of any integer.
Step-by-step explanation:
The expression x²-8 is not a difference of perfect squares. A difference of perfect squares takes the form a² - b², where both a and b are perfect squares. In the expression given, x² is a perfect square, but -8 is not, as there is no integer that when squared gives -8. Hence, we cannot factor this expression as a difference of perfect squares.