Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Applications of Derivatives

Question:

If $f(x)=\int\limits_x^{x^2} \frac{1}{(\log t)^2} d t, x \neq 0, x \neq 1$ then f(x) is monotomically

Options:

increasing on (2, ∞)

increasing on (1, 2)

decreasing on (2, ∞)

decreasing on (0, 3)

Correct Answer:

increasing on (2, ∞)

Explanation:

We have,

$f(x) =\int\limits_x^{x^2} \frac{1}{(\log t)^2} d t$

$\Rightarrow f'(x) =2 x \frac{1}{\left(\log x^2\right)^2}-\frac{1}{(\log x)^2}=\left(\frac{x-2}{2}\right) \times \frac{1}{(\log x)^2}$

Clearly, f'(x) > 0 for all x > 2.

Hence, f(x) is increasing on (2, ∞).