To compare \( \sqrt{21} \) and \( \sqrt{17} \) using rational approximations, we can start by estimating their square roots.
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We know that \( \sqrt{16} = 4 \) and \( \sqrt{25} = 5 \). This means: \[ 4 < \sqrt{17} < 5 \]
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For \( \sqrt{21} \): \[ \sqrt{21} > 4 \quad \text{(since \( 21 > 16 \))} \] \[ \sqrt{21} < 5 \quad \text{(since \( 21 < 25 \))} \] Therefore: \[ 4 < \sqrt{21} < 5 \]
Now we can use rational approximations to get a better idea of the values.
If we calculate more precise approximations:
- \( \sqrt{17} \) is approximately \( 4.123 \).
- \( \sqrt{21} \) is approximately \( 4.583 \).
Since \( \sqrt{21} \approx 4.583 \) is greater than \( \sqrt{17} \approx 4.123 \), we can conclude: \[ \sqrt{21} > \sqrt{17} \]
Thus, the answer is: \[ \sqrt{21} > \sqrt{17} \]