Find the critical numbers of the function

Question

f(x)=x^(1/6)−x^(−5/6)

Answer 1

f = x^(1/6)−x^(−5/6)
f' = (1/6)x^(-5/6) + (5/6)x^(-11/6)
= (1/6)x^(-11/6)(x+5)

so, where is f' = 0?