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The function f(x) = x/2 + 2/x has a local minimum at

1. x = 2
2. x = -2
3. x = 0
4. x = 1

Correct answer: x = 2

Solution

f'(x)=1/2-2/x^2=0 -> x=+-2. f''(x)=4/x^3>0 at x=2, so the local minimum is at x=2.

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