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## Determine if these real numbers are rational II

Our main tool is Corollary 2.3.

Solution: We only show that $\sqrt[5]{7}$ is irrational.

Clearly, $\sqrt[5]{7}$ is a solution of $x^5-7=0$. Hence by Corollary 2.3, the rational solution to this equation can only be $\pm 1$ and $\pm 7$. It is straightforward to check that none of them are solutions of $x^5-7=0$. Hence $x^5-7=0$ does not have rational solutions and $\sqrt[5]{7}$ is irrational.

The rests are similar.