$3-$ In the power system below, we have $2$ s V V $$ and $2$ r V V $.$ Once the switch K is open, the active power passing through the line is $0$ P $.$ Once the switch K is closed, the voltage source $0$ m V V $$ is added to the system. In this case the active power passing through the line $($between bus $1$ and $3)$ becomes $1$ P $.$ Prove that $01$ cos $2$ P P $.$ Does the voltage source m V consume, generate or neither consume nor V change the active power flow of the line? If generate active power? Did the presence of voltage source m so$,$ how?