To simplify the radical expression (45^5n), we can break it down as follows:

(45^5n) = (45^4 * 45 * n)

Now, we can simplify the expression inside the radical by taking out perfect squares:

(45^4 * 45 * n) = ((9^2 * 5^4) * 45 * n)

Using the property of radicals, we can split the radical into separate radicals for each factor:

((9^2 * 5^4) * 45 * n) = (9 * 5^2) * (45 * n)

Simplifying the expression further:

(9 * 5^2) * (45 * n) = 45 * (45n)

Therefore, the simplified form of the radical expression (45^5n) is 45 (45n).