To solve this inequality, we need to simplify both sides and then compare them.

First, let's simplify the left side of the inequality:

(3/5)^3 x^2 - 1 >= (9/25)^13
(27/125) x^2 - 1 >= (3/5)^26
(27/125) x^2 - 1 >= (3^26) / (5^26)
(27/125) x^2 - 1 >= 1 / (5^26 / 3^26)
(27/125) * x^2 - 1 >= 1 / (3/5)^26

Now, let's simplify the right side of the inequality:

(9/25)^13
(3/5)^26

Now, let's compare the simplified left and right sides:

(27/125) * x^2 - 1 >= 1 / (3/5)^26

This is our final simplified inequality.