Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Continuity and Differentiability

Question:

If $\underset{x→0}{\lim}(1+ax+bx^2)^{2/x}=e^3$, then

Options:

a = 3, b = 0

a = 3/2, b  1

a = 3/2, b = 4

a = 2, b = 3

Correct Answer:

a = 3/2, b = 4

Explanation:

$\underset{x→0}{\lim}(1+ax+bx^2)^{2/x}=\underset{x→0}{\lim}(1+ax+bx^2)^{\frac{1}{ax+bx^2}\frac{2(ax+bx^2)}{x}}$

$=e^{\underset{x→0}{\lim}\frac{2(ax+bx^2)}{x}}e^{2a}=e^3⇒a=\frac{3}{2}$, b any real number.

Hence (C) is the correct answer.