The frequency of oscillation of the springs shown in fig (4) will be

Here x1=−F/k1  and  x2=−F/k2Total extension x=x1+x2=−F1k1+1k2we know that F = - k  x k=k1k2k1+k2 Further T=2π(m/k) =2πmk1+k2k1k2 n=1T=12πk1k2mk1+k2