Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Definite Integration

Question:

If $I_1=\int\limits_{e}^{e^2}\frac{dx}{\log x}$ and $I_2=\int\limits_{1}^{2}\frac{e^x}{x}dx$, then

Options:

$I_1=I_2$

$2I_1=I_2$

$I_1=2I_2$

none of these

Correct Answer:

$I_1=I_2$

Explanation:

$I_2=\int\limits_{1}^{2}\frac{e^x}{x}dx$

let $y=e^x⇒dy=e^xdx$

so $x=\log y$

as $x → 1, y → e$

$x → 2, y → e^2$

$I_2=\int\limits_{e}^{e^2}\frac{dy}{\log y}$

$⇒I_2=\int\limits_{e}^{e^2}\frac{dx}{\log x}=I_1$