Simplify 125^(-2/3)

Simplify 125^-2/3
A negative indices means that we need to reciprocate the number or "flip it":
125^-2/3 = (1/125)^2/3
A fractional indices can be split up based on the denominator and numerator. Here, the denominator is 3 so we must cube root the number and the numerator is 2 so then we must square the number. This looks like this:
(1/125)^2/3 = (1/5)² = 1/25