Question:medium

For real \(x\), the maximum possible value of \(\frac{x}{\sqrt{1+x^4}}\) is

Updated On: Jun 26, 2026
  • \(\frac{1}{\sqrt3}\)
  • 1
  • \(\frac{1}{\sqrt2}\)
  • \(\frac{1}{2}\)
Show Solution

The Correct Option is C

Solution and Explanation

To determine the maximum value of \(\frac{x}{\sqrt{1+x^4}}\), we define the function \(f(x) = \frac{x}{\sqrt{1+x^4}}\). We will employ calculus to find its maximum.

First, we compute the derivative \(f'(x)\) using the quotient rule: If \(f(x) = \frac{u}{v}\), then \(f'(x) = \frac{v \cdot u' - u \cdot v'}{v^2}\). Here, \(u = x\) and \(v = \sqrt{1+x^4}\).

Consequently, \(u' = 1\) and \(v' = \frac{4x^3}{2\sqrt{1+x^4}} = \frac{2x^3}{\sqrt{1+x^4}}\).

Substituting these into the quotient rule yields: \(f'(x) = \frac{\sqrt{1+x^4} \cdot 1 - x \cdot \frac{2x^3}{\sqrt{1+x^4}}}{1+x^4}\)

\(\frac{\sqrt{1+x^4} - \frac{2x^4}{\sqrt{1+x^4}}}{1+x^4}\)

\(\frac{(\sqrt{1+x^4})^2 - 2x^4}{(1+x^4)\sqrt{1+x^4}}\)

\(\frac{1+x^4 - 2x^4}{(1+x^4)\sqrt{1+x^4}}\)

\(\frac{1-x^4}{(1+x^4)\sqrt{1+x^4}}\).

Setting \(f'(x) = 0\) produces \(1-x^4 = 0\), which implies \(x^4 = 1\). The critical points are therefore \(x = \pm1\).

We evaluate \(f(x)\) at these critical points:

For \(x = 1\)\(f(1) = \frac{1}{\sqrt{1+1^4}} = \frac{1}{\sqrt{2}}\).

For \(x = -1\)\(f(-1) = \frac{-1}{\sqrt{1+(-1)^4}} = -\frac{1}{\sqrt{2}}\).

The maximum value attained is \(\frac{1}{\sqrt{2}}\).

Thus, the maximum possible value of \(\frac{x}{\sqrt{1+x^4}}\) is \(\frac{1}{\sqrt{2}}\).

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