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in Derivatives by (28.3k points)
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The minimum value of \(\frac{x}{log_ex}\) is :

A . e 

B. 1/e 

C. 1 

D. none of these

1 Answer

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Best answer

Option : (A) 

f(x) = \(\frac{x}{log x}\)

f'(x) = \(\frac{log x-1}{(logx)^2}\)

f’(x) = 0

\(\frac{log x-1}{(logx)^2}\) = 0

log x -1 = 0

⇒ x = e 

for second derivative we find f’(x)

Hence by second derivative test 

f’’(x) > 0 

So it’s a point of minimum. 

Therefore,

f''(e) = \(\frac{-1}{e(loge)^2}+\)\(\frac{2}{e(loge)^2}\)

\(-(\frac{1}{e})+(\frac{2}{e})\)

⇒ \(\frac{1}{e}\) > 0

x = e is a point of minimum

So, minimum value is f(e) = e

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