For $x<0$, $|x|=-x$ so $f(x)=\dfrac{x}{-x}=-1$ (constant) ⇒ continuous.
For $x>0$, $f(x)=-1$ ⇒ continuous.
At $x=0$:
$\displaystyle \lim_{x\to0^-} f(x)=-1,\quad \lim_{x\to0^+} f(x)=-1,\quad f(0)=-1$
Hence $f$ is continuous at $x=0$.
Therefore, $f$ is continuous for all real $x$.
A function f(x) is defined as $$f(x)=\begin{cases}{\frac{1-\cos 4x}{{x}^2}} & {;x{\lt}0} \\ {a} & {;x=0} \\ {\frac{\sqrt[]{x}}{\sqrt[]{(16+\sqrt[]{x})-4}}} & {;x{\gt}0}\end{cases}$$
if the function f(x) is continuous at x = 0, then the value of a is: