I hope I got the correct exercise.
5/3[x^(2/3)] - 10/3[x^(-1/3)]
so the powers are only for the x, not for the 3 as well
5/3[x^(2/3)] - 10/3[x^(-1/3)] = 5/3x^(-1/3) * (x-2)
You take the factor 5/3x^(-1/3) out in front of the parentheses. Then what you want to calculate is the following:
1. {5/3[x^(2/3)]} / {5/3[x^(-1/3)]} = x - I hope this is obvious considering the fact that the terms are identical with the exception of the power of x. Considering one is 2/3 and the other is -1/3 and you will subtract them, the power of x will be 2/3-(-1/3) = 2/3 + 1/3 = 1
2. {10/3[x^(-1/3)]} / {5/3[x^(-1/3)]} = 2 - this should also be obvious because the powers are identical, the only difference is the top term, which leads us to 10/5 = 2 as a result
When combined you can see that if you take 5/3x^(-1/3) out, then the first factor remains as x, the second factor remains as 2, and the sign between them is "-".
Conclusion: 5/3[x^(2/3)] - 10/3[x^(-1/3)] = 5/3x^(-1/3) * (x-2) = x * 5/3x^(-1/3) - 2 * 5/3x^(-1/3) = 5/3[x^(2/3)] - 10/3[x^(-1/3)] TRUE. Q.E.D.