3. Find the local maxima and local minima, if any, of the following functions. Find
also the local maximum and the local minimum values, as the case may be:

(vi) g ( x) = \frac{x}{2} + \frac{2}{x} , x > 0

Answers (1)

Given function is
g ( x) = \frac{x}{2} + \frac{2}{x}\\ g^{'}(x) = \frac{1}{2}-\frac{2}{x^2}\\ g^{'}(x) = 0\\ \frac{1}{2}-\frac{2}{x^2} = 0\\ x^2 = 4\\ x = \pm 2            ( but as x > 0 we only take the positive value of x i.e. x = 2)
Hence, 2 is the only  critical point
Now, we use the second derivative test
g^{''}(x) = \frac{4}{x^3}\\ g^{''}(2) = \frac{4}{2^3} =\frac{4}{8} = \frac{1}{2}> 0
Hence, 2 is the point of minima and the minimum value is 
g ( x) = \frac{x}{2} + \frac{2}{x} \\ g(2) = \frac{2}{2} + \frac{2}{2} = 1 + 1 = 2


 

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