x2 − 225 = 0

This is a quadratic equation. To solve for x, we can use the difference of squares formula:

x^2 - 225 = (x + 15)(x - 15) = 0

So either (x + 15) = 0 or (x - 15) = 0. Solving for x gives us:

x = -15 or x = 15

Therefore, the solutions to the equation are x = -15 and x = 15.