(c)
Since, $f(x) = \frac{1 - \tan x}{4x - \pi}$
Now, $\lim_{x \rightarrow \pi/4}{f(x) = \lim_{x \rightarrow \pi/4}\left( \frac{1 - \tan x}{4x - \pi} \right)}$
$= \lim_{x \rightarrow \pi/4}\ \left( \frac{–\sec^{2}x}{4} \right) = - \frac{1}{2}$
Since, $f(x)$ is continuous at
$x = \frac{\pi}{4}$
$\therefore\ \ \ \lim_{x \rightarrow \pi/4}{f(x)} = f\left( \frac{\pi}{4} \right) = - \frac{1}{2}$