MCQ
If $f (x)=\left\{\begin{array}{ll}\frac{\sin 3 x}{ e ^{2 x}-1} & ; x \neq 0 \\ k -2 & ; x=0\end{array}\right.$ is continuous at $x=0$, then $k =$
  • A
    $\frac{9}{5}$
  • B
    $\frac{2}{3}$
  • $\frac{7}{2}$
  • D
    $\frac{1}{2}$

Answer

Correct option: C.
$\frac{7}{2}$
(C)
f is continuous at $x=0$
$\Rightarrow \lim _{x \rightarrow 0} f(x)=f(0)$
$\Rightarrow \lim _{x \rightarrow 0} \frac{\sin 3 x}{ e ^{2 x}-1}= k -2$
$\Rightarrow \lim _{x \rightarrow 0} \frac{\frac{\sin 3 x}{x}}{\frac{ e ^{2 x}-1}{x}}= k -2$
$\Rightarrow \frac{3 \lim _{x \rightarrow 0} \frac{\sin 3 x}{3 x}}{2 \lim _{x \rightarrow 0} \frac{ e ^{2 x}-1}{2 x}}= k -2$
$\Rightarrow \frac{3}{2}= k -2$
$\Rightarrow k=\frac{7}{2}$

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