2 answers
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5^(1/3) + 5^(-1/3)
= 5^(1/3) + 1 / 5^(1/3) * 5(2/3)/5^(2/3)
= 5(1/3) + 5^(2/3) / 5
hope this is what you meant, there is no longer any irrational
number in the denominator.