If \(f\left( x\right) =\left\{ \left| x\right| \cos \begin{pmatrix} \dfrac{1}{x} \\ k \end{pmatrix}+9x^2 \begin{matrix} \rm{if} \ x \ne 0 \\\ \rm{if}\ x = 0 \end{matrix}\right\}\) then f is continuous if the value of k is: