Answer: We can check whether the expression (x + 18) is a factor of x² - 324 by dividing x² - 324 by (x + 18) using polynomial long division or synthetic division.
Using polynomial long division:
x + 18 │x² + 0x - 324
-x² - 18x
----------
18x - 324
18x + 324
----------
0
Since there is no remainder, we can see that (x + 18) is indeed a factor of
x² - 324.