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If \(4x^{2} + \frac{1}{4x^{2}} = 14\), what is the positive value of \(x + \frac{1}{4x}\)?

This question was previously asked in
RRB ALP 2025 CBT 2 Wiremen Question Paper (28-Jul-2026) (Shift 2)
The correct answer is
2

Algebraic Solution for \(x + \frac{1}{4x}\)

We are given the equation \(4x^{2} + \frac{1}{4x^{2}} = 14\). We need to find the positive value of the expression \(x + \frac{1}{4x}\).

Using Algebraic Identities

Consider the algebraic identity \((a+b)^2 = a^2 + 2ab + b^2\). Let's choose \(a = 2x\) and \(b = \frac{1}{2x}\).

  • \(a^2 = (2x)^2 = 4x^2\)
  • \(b^2 = (\frac{1}{2x})^2 = \frac{1}{4x^2}\)
  • \(2ab = 2(2x)(\frac{1}{2x}) = 2\)

Therefore, we can write:

\( \left(2x + \frac{1}{2x}\right)^2 = (2x)^2 + 2(2x)\left(\frac{1}{2x}\right) + \left(\frac{1}{2x}\right)^2 \) \( \left(2x + \frac{1}{2x}\right)^2 = 4x^2 + 2 + \frac{1}{4x^2} \)

Rearranging terms, we get:

\( \left(2x + \frac{1}{2x}\right)^2 = \left(4x^2 + \frac{1}{4x^2}\right) + 2 \)

Calculating Intermediate Value

Substitute the given value \(4x^2 + \frac{1}{4x^2} = 14\) into the equation:

\( \left(2x + \frac{1}{2x}\right)^2 = 14 + 2 \) \( \left(2x + \frac{1}{2x}\right)^2 = 16 \)

To find the value of \(2x + \frac{1}{2x}\), take the square root of both sides:

\( 2x + \frac{1}{2x} = \pm\sqrt{16} \) \( 2x + \frac{1}{2x} = \pm 4 \)

Since \(x\) is typically assumed positive in such problems for a positive result, both \(2x\) and \(\frac{1}{2x}\) are positive. Thus, their sum must be positive.

\( 2x + \frac{1}{2x} = 4 \)

Finding the Final Value

Now, let's relate the expression we need, \(x + \frac{1}{4x}\), to the value we just found.

Factor out \(\frac{1}{2}\) from the expression \(x + \frac{1}{4x}\):

\( x + \frac{1}{4x} = \frac{1}{2} \left( 2x + \frac{1}{2x} \right) \)

Substitute the value \(2x + \frac{1}{2x} = 4\):

\( x + \frac{1}{4x} = \frac{1}{2} (4) \) \( x + \frac{1}{4x} = 2 \)

The positive value of \(x + \frac{1}{4x}\) is 2.

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