If $f(x)=\left\{\begin{array}{cl}\frac{\sin 3 x}{x}, & \text { if } x \neq 0 \\ \frac{k}{2}, & \text { if } x=0\end{array}\right.$ is continuous at $x=0$, then $k$ is equal to_____________
The given function $f(x)=\left\{\begin{array}{cl}\frac{\sin 3 x}{x}, & \text { if } x \neq 0 \\ \frac{k}{2}, & \text { if } x=0\end{array}\right.$ is continuous at $x=0$
$\therefore f(0)=\lim _{x \rightarrow 0} f(x)$
$\Rightarrow \frac{k}{2}=\lim _{x \rightarrow 0} \frac{\sin 3 x}{x}$
$\Rightarrow \frac{k}{2}=3 \lim _{x \rightarrow 0} \frac{\sin 3 x}{3 x}$
$\Rightarrow \frac{k}{2}=3 \times 1=3$ $\left(\lim _{x \rightarrow 0} \frac{\sin x}{x}=1\right)$
$\Rightarrow k=6$
Thus, the value of k is 6.
If $f(x)=\left\{\begin{array}{ll}\frac{\sin 3 x}{x}, & \text { if } x \neq 0 \\ \frac{k}{2}, & \text { if } x=0\end{array}\right.$ is continuous at $x=0$, then $k$ is equal to ___6____.