A system consists of two springs connected in series and having the stiffness coefficients `k_1` and `k_2`. Find the minimum work to be performed in order to stretch this system by `Deltal`.

Explanation

Since the springs are connected in series, the combination may be treated as a single spring of spring constant.
`k=(k_1k_2)/(k_1+k_2)`
From the equation of increment of `M.E.`, `DeltaT+DeltaU=A_(ext)`
`0+1/2kDeltat^2=A`, or, `A=1/2((k_1k_2)/(k_1+k_2))Deltal^2`