If $f(x)=\left\{\begin{array}{cc}\frac{k \cos x}{\pi-2 x}, & x \neq \frac{\pi}{2} \\ 3, & x=\frac{\pi}{2}\end{array}\right.$ is continuous at $x=\frac{\pi}{2}$, then k is :
Answer & explanation
Correct answer: option 1
$f(x)=\left\{\begin{array}{cc}
\frac{k \cos x}{\pi-2 x} & x \neq \frac{\pi}{2} \\
3 & x=\frac{\pi}{2}
\end{array}\right.$
f(x) is continuous at $x=\frac{\pi}{2}$
$f(\frac{\pi}{2})=3$
$\lim\limits_{x \rightarrow \frac{\pi}{2}} f(x)=\lim\limits_{x \rightarrow \frac{\pi}{2}} \frac{k \cos x}{\pi-2 x}$
Using L' hospital rule (differentiating numeration and denominator separately)
$\Rightarrow \lim\limits_{x \rightarrow \frac{\pi}{2}} \frac{-k \sin x}{-2}$
$=\frac{k \sin \frac{\pi}{2}}{2}=\frac{k}{2}$
so $\lim\limits_{x→\frac{\pi}{2}} f(x) = f(\frac{\pi}{2})$
⇒ $k = \frac{k}{2}=3$
k = 6