The function \(f(x) = x + \displaystyle\frac{a^2}{x}, a \gt 0, x \ne 0\) has a local maxima at
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \(x = -a\)
A local maximum occurs at a critical point where the second derivative is negative (second derivative test).
\( \displaystyle f'(x) = 1 - \frac{a^2}{x^2} \)
Putting \(f'(x) = 0\):
\(x^2 = a^2\)
\(x = a \text{ or } x = -a\)
\( \displaystyle f''(x) = \frac{2a^2}{x^3} \)
At \(x = -a\):
\( \displaystyle f''(-a) = \frac{2a^2}{-a^3} = -\frac{2}{a} \lt 0 \)
So f has a local maximum at \(x = -a\).
At \(x = a\):
\( \displaystyle f''(a) = \frac{2a^2}{a^3} = \frac{2}{a} \gt 0 \)
So \(x = a\) gives a local minimum, not a maximum.