To determine whether each of the following expressions is rational, we review them one by one.
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\( 13\sqrt{1} \): This simplifies to \( 13 \), which is a rational number.
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\( \frac{1}{\sqrt{3}} \): This expression is not rational because it involves the square root of 3, which is an irrational number.
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\( 3\sqrt{3} \times \sqrt{3} \): Simplifying this gives us \( 3 \times 3 = 9 \), which is rational.
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\( 3\sqrt{3} + \sqrt{3} \): This simplifies to \( (3 + 1)\sqrt{3} = 4\sqrt{3} \), which is not rational because it includes the irrational number \( \sqrt{3} \).
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\( \sqrt[3]{1} \): This simplifies to \( 1 \), which is rational.
In summary, the rational expressions among the options given are:
- \( 13\sqrt{1} \) (which equals 13)
- \( 3\sqrt{3} \times \sqrt{3} \) (which equals 9)
- \( \sqrt[3]{1} \) (which equals 1)
Therefore, the rational options are \( 13\sqrt{1} \), \( 3\sqrt{3} \times \sqrt{3} \), and \( \sqrt[3]{1} \).