If $f:R \to R$ is defined by $f(x) = \left\{ \begin{array}{l l} \frac{2 sin x-\sin 2x}{2x \cos x}, & \quad if \;x \neq 0 \\ a, & \quad if \; x =0 \end{array} \right.$ then the value of $a$ so that f is continuous at 0 is :

Question

$$\begin {array} {1 1} (1)\;2 & \quad (2)\;1 \\ (3)\;-1 & \quad (4)\;0 \end {array}$$