A generator delivers power of 1 p.u. to an infinite bus through a purely reactive network. The maximum power that could be delivered by the generator is 2.0 p.u. A three-phase fault occurs at the terminals of the generator which reduces the generator output to zero. The fault is cleared after t_c seconds. The original network is then restored. The maximum swing of the rotor angle (δ) of the generator is found to be δ_max = 120 electrical degrees. The value of cos δ at time t = t_c is