logax = r <=> a^r = x
log[(1/5)^(1/3)] 125 = r <=> {[(1/5)^(1/3)]^r}=125
{[(1/5)^(1/3)]^r} = 5^3
{[5^(-1)]^(1/3)}^r = 5^3
[5^(-1/3)]^r = 5^3
5^(-r/3) = 5^3
-r/3 = 3
-r = 9
r = -9