The function f is defined by \(f(x) = 2x + (x + 1)^{-2}\) for \(x > -1\).
Find \(f'(x)\) and \(f''(x)\) and hence verify that the function f has a minimum value at \(x = 0\).
Solution
First, find the first derivative \(f'(x)\):
\(f'(x) = \frac{d}{dx}[2x + (x + 1)^{-2}] = 2 - 2(x + 1)^{-3}\).
Next, find the second derivative \(f''(x)\):
\(f''(x) = \frac{d}{dx}[-2(x + 1)^{-3}] = 6(x + 1)^{-4}\).
Evaluate \(f'(x)\) at \(x = 0\):
\(f'(0) = 2 - 2(1)^{-3} = 0\).
This shows that \(x = 0\) is a stationary point.
Evaluate \(f''(x)\) at \(x = 0\):
\(f''(0) = 6(1)^{-4} = 6 > 0\).
Since \(f''(0) > 0\), the function has a minimum at \(x = 0\).
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