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If $\left(\text{a}^2 + \frac{1}{\text{a}^2}\right) = 18$ then find $\left(\text{a} - \frac{1}{\text{a}}\right)$

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper PDF (31-Jan-2021) (Shift 1)
The correct answer is
4

To solve the problem, we need to find the value of \(\left(a - \frac{1}{a}\right)\) given that \(\left(a^2 + \frac{1}{a^2}\right) = 18\).

We begin by using the identity:

\(a^2 + \frac{1}{a^2} = \left(a - \frac{1}{a}\right)^2 + 2.\)

Given that \(a^2 + \frac{1}{a^2} = 18\), we can write:

\(\left(a - \frac{1}{a}\right)^2 + 2 = 18\)

Simplifying the equation, we get:

\(\left(a - \frac{1}{a}\right)^2 = 18 - 2\)

\(\left(a - \frac{1}{a}\right)^2 = 16\)

Taking the square root on both sides, we find:

\(\left(a - \frac{1}{a}\right) = \pm 4\)

The problem does not specify whether \(a\) is positive or negative, but typically in such questions, we consider the principal (positive) value. Therefore,:

\(a - \frac{1}{a} = 4\)

Thus, the correct answer is 4.

Based on the analysis and calculation above, the correct option is 4.

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