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Mathematics · 2024 · 3 marks
CBSE 2024 · Region 4 · Set 1 · Q30
Prove that $\displaystyle \frac{2-\sqrt{3}}{5}$ is an irrational number, given that $\displaystyle \sqrt{3}$ is an irrational number.
Marking-scheme solution
Assuming \(\displaystyle \frac{2-\sqrt{3}}{5}\) to be a rational number.
\[\begin{aligned}
& \Rightarrow \frac{2-\sqrt{3}}{5}=\frac{p}{q}, u \\
& \Rightarrow \sqrt{3}=\frac{2 q-5 p}{q}
\end{aligned}
\]
Here RHS is rational but LHS is irrational.
Therefore our assumption is wrong.
Hence \(\displaystyle \frac{2-\sqrt{3}}{5}\) is an irrational number.
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CBSE Class 10 Mathematics past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.