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Question

$16(x^4 + \frac{1}{x^4}) - 257 = 0$

What is \(\left(x^2 + \frac{1}{x^2}\right)\) equal to ?

This question was previously asked in
CDS 2 2026 Maths Question Paper (13-Sep-2026)
The correct answer is

\(\frac{17}{4}\)

To solve the problem, we need to find the value of \(x^2 + \frac{1}{x^2}\) given the equation:

\(16(x^4 + \frac{1}{x^4}) - 257 = 0.\)

Let's proceed step-by-step:

  1. \(16(x^4 + \frac{1}{x^4}) = 257\)
  2. Simplifying, we get:
    • \(x^4 + \frac{1}{x^4} = \frac{257}{16}\)
  3. Recall the identity:
    • \((x^2 + \frac{1}{x^2})^2 = x^4 + \frac{1}{x^4} + 2\)
  4. Now, substitute the value we found:
    • \((x^2 + \frac{1}{x^2})^2 = \frac{257}{16} + 2\)
  5. Convert and simplify:
    • \(\frac{257}{16} + 2 = \frac{257}{16} + \frac{32}{16} = \frac{257 + 32}{16} = \frac{289}{16}\)
  6. Thus,
    • \((x^2 + \frac{1}{x^2})^2 = \frac{289}{16}\)
  7. Taking the square root on both sides gives:
    • \(x^2 + \frac{1}{x^2} = \sqrt{\frac{289}{16}} = \frac{\sqrt{289}}{\sqrt{16}} = \frac{17}{4}\)

Finally, the correct answer to the problem according to computations and given options is \(\frac{17}{4}\)

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