A precision mechanical system is designed such that the energy dissipated during each successive oscillation follows a geometric progression. Let the energy dissipated in the $n$-th oscillation be $u_n$.

Given that:

• the total energy dissipated over an infinite number of oscillations is 25 Joules
• the cumulative energy dissipated during the first three oscillations is 23.4 Joules

find, for this sequence,