I have been trying to find a solution to the following problem.

x^{(4/3) }- x^{(-2/3) }+ c = 0 where -1 < x > 1

I think if I could solve,

s^{(-2)}- s + c = 0,

I could use substitution to solve the first equation, but I have not had any luck with the second either.

Any help would be appreciated.