Final answer:
The expression that can be simplified as 1/n^18 is (n-3)^6.
Step-by-step explanation:
The expression that can be simplified as 1/n^18 is (n-3)^6.
To simplify this expression, we can use the rule that states (a-b)^n = (a^n) * (b^n), where n is the exponent. Applying this rule to (n-3)^6, we get (n^6) * (-3^6) = n^6 * 729.
Therefore, the expression 1/n^18 simplifies to 1/n^(6+12) = 1/n^6 * n^12 = n^12/n^6 = n^(12-6) = n^6.