Question
The minimum value of $(\text{x}^{2}+\frac{250}{\text{x}})$ is:
  1. 75
  2. 50
  3. 25
  4. 55

Answer

  1. 75

Sloution:

$\text{f}(\text{x})=\text{x}^{2}+\frac{250}{\text{x}}$

$\text{f}'(\text{x})=2\text{x}-\frac{250}{\text{x}^{2}}$

For the local minima a or maxima. We must have f'(x) = 0

 $=2\text{x}-\frac{250}{\text{x}^{2}}=0$

⇒ x = 5

$=2\text{x}-\frac{250}{\text{x}^{2}}=0$

$\text{f}''(\text{x})=2+\frac{500}{\text{x}^{3}}$

$\text{f}''(\text{x})=2+\frac{500}{125}>0$

function has minima at x = 5

f(5) = 75.

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