If $f :R \to R$ defined by $f(x)= \left\{ \begin{array}{1 1} \frac{1+3x^2-\cos 2x}{x^2}, & \quad for\; x \neq 0 \\ k & \quad for \; x=0 \end{array}. \right.$ is continuous at x=0, then k=

Question

$$\begin {array} {1 1} (1)\;0 & \quad (2)\;5 \\ (3)\;6 & \quad (4)\;0 \end {array}$$