Maxima and Minima — Maths STD 12 Science — Question
Gujarat BoardEnglish MediumSTD 12 ScienceMathsMaxima and Minima2 Marks
Question
Write the minimum value of $\text{f}(\text{x})=\text{x}+\frac{1}{\text{x}},\text{x}>0.$
✓
Answer
Given, $\text{f}\text{(x)}=\text{x}+\frac{1}{\text{x}}$ $\therefore\ \text{f}'\text{(x)}=1-\frac{1}{\text{x}^2}$ For a local maxima or a local minima, $\text{f}'\text{(x)}=0$ $\Rightarrow1-\frac{1}{\text{x}^2}=0$ $\Rightarrow\text{x}= +1,-1$ Now, $\text{f}''(\text{x})=\frac{2}{\text{x}^{3}}$ At x = 1, f''(x) x = -1, f''(x) = -2 < 0 $\therefore $ x = -1 is point of local minima $\therefore $ maximum value of = f(-1) = -2.
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