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Question

If $x = 2 + \sqrt{3}$, find $x - \frac{1}{x}$.

This question was previously asked in
SSC CGL 2025 Tier 2 Paper 1 Question Paper (19-Jan-2026)
The correct answer is
$2\sqrt{3}$

Calculate $\frac{1}{x}$

Given the value of $x$ is $2 + \sqrt{3}$. To find $\frac{1}{x}$, we calculate the reciprocal:

$ \frac{1}{x} = \frac{1}{2 + \sqrt{3}} $

To simplify this fraction, we multiply the numerator and the denominator by the conjugate of the denominator, which is $2 - \sqrt{3}$:

$ \frac{1}{x} = \frac{1}{2 + \sqrt{3}} \times \frac{2 - \sqrt{3}}{2 - \sqrt{3}} $

Using the difference of squares formula $(a+b)(a-b) = a^2 - b^2$ for the denominator:

$ \frac{1}{x} = \frac{2 - \sqrt{3}}{2^2 - (\sqrt{3})^2} = \frac{2 - \sqrt{3}}{4 - 3} = \frac{2 - \sqrt{3}}{1} $

Therefore, $\frac{1}{x} = 2 - \sqrt{3}$.

Calculate $x - \frac{1}{x}$

Now, substitute the values of $x$ and $\frac{1}{x}$ into the expression $x - \frac{1}{x}$:

$ x - \frac{1}{x} = (2 + \sqrt{3}) - (2 - \sqrt{3}) $

Distribute the negative sign:

$ x - \frac{1}{x} = 2 + \sqrt{3} - 2 + \sqrt{3} $

Combine like terms:

$ x - \frac{1}{x} = (2 - 2) + (\sqrt{3} + \sqrt{3}) $ $ x - \frac{1}{x} = 0 + 2\sqrt{3} $

Thus, the final value is $2\sqrt{3}$.

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Important Questions from Surds and Indices

  1. The value of \(\frac{{{{\left( {251} \right)}^3} + {{\left( {249} \right)}^3}}}{{25.1 \times 25.1 - 624.99 + 24.9 \times 24.9}}\)  is 5 × 10 , where the value of k is :

  2. Find the value of m in \(\left(\frac{2}{7}\right)^{-3} \times \left(\frac{2}{7}\right)^{-5}=\left (\frac{2}{7}\right)^{-3m+1}\)

  3. If √625 = 25; then√(.00000625/25)is:

    A. 0.0025

    B. 0.001

    C. 0.0001

    D. 0.0005
  4. Find the value of:

    \(\sqrt{150}-\sqrt{54}-\sqrt{24}\)

  5. If \(\sqrt{4624}=68\) , then the value of:

    \(\sqrt{46.24}+\sqrt{0.4624}+\sqrt{0.004624}\)

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