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Mathematics · 2023 · 2 marks
CBSE 2023 · Region 2 · Set 1 · Q21
Prove that 2+√ 3 is an irrational number, given that √ 3 is an irrational number.
Prove that $\displaystyle 2+\sqrt{3}$ is an irrational number, given that $\displaystyle \sqrt{3}$ is an irrational number.
Marking-scheme solution
Let us assume that \(\displaystyle 2+\sqrt{3}\) is rational
Let \(\displaystyle 2+\sqrt{3}=\frac{\mathrm{p}}{\mathrm{q}} ; \mathrm{q} \neq 0\) and p, q are integers
\[\Rightarrow \sqrt{3}=\frac{p-2 q}{q}
\]
p and q are integers, \(\displaystyle \therefore \mathrm{p}-2 \mathrm{q}\) is an integer
\(\displaystyle \Rightarrow \frac{\mathrm{p}-2 \mathrm{q}}{\mathrm{q}}\) is a rational number
\(\displaystyle \Rightarrow \sqrt{3}\) is a rational number which contradicts our assumption that \(\displaystyle \sqrt{3}\) is an irrational number.
\(\displaystyle \Rightarrow 2+\sqrt{3}\) is an irrational number
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