In arrangement given in fig. (8), if the block of mass m is displaced, the frequency is given by 
 

Let the extension in spring A is x, then the compression in string B will also be x. The restoring force on mass is a force given by .k, x. This force acts towards left' Again a force k₂, x pushes the mass to the left due to compression of spring B. The net restoring force acting on the mass is $\left(k_1+k_2\right)x$
$$\begin{gathered} \text{ force constant }=\left({\mathrm{k}}_1+{\mathrm{k}}_2\right) \\ \mathrm{Now} \mathrm{T}=2\mathrm{\pi }\sqrt{\left(\frac{\mathrm{m}}{{\mathrm{k}}_1+{\mathrm{k}}_2}\right)} \\ \text{ Frequency }\mathrm{n}=\frac{1}{\mathrm{T}}=\frac{1}{2\mathrm{\pi }}\sqrt{\left\{\frac{\left({\mathrm{k}}_1+{\mathrm{k}}_2\right)}{\mathrm{m}}\right\}} \end{gathered}$$