Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section A

Chapter

Applications of Derivatives

Question:

The function $f(x)=x^x$ decreases on the interval

Options:

$(0, e)$

$(0, 1)$

$(0,\frac{1}{e})$

None of these

Correct Answer:

$(0,\frac{1}{e})$

Explanation:

Clearly, f(x) is defined for x > 0

Now, $f(x)=x^x⇒f'(x)=x^x(1+\log x)$

For to be decreasing, we must have

$f'(x)<0⇒x^x(1+\log x)<0$

$⇒1+\log x<0⇒\log x< -1 ⇒ x<e^{-1}$

So, f(x) is decreasing on $(0,\frac{1}{e})$