Two identical capacitors have same capacitance $C$. One of them is charged to the potential $V$ and other to the potential $2V$. The negative ends of both are connected together. When the positive ends are also joined together, the decrease in energy of the combined system is:\\
(1) $\frac { 1 } { 4 } C V ^ { 2 }$\\
(2) $2 C V ^ { 2 }$\\
(3) $\frac { 1 } { 2 } C V ^ { 2 }$\\
(4) $\frac { 3 } { 4 } C V ^ { 2 }$