A wire of length $L$ is hanging from a fixed support. The length changes to $L _ { 1 }$ and $L _ { 2 }$ when masses 1 kg and 2 kg are suspended respectively from its free end. Then the value of $L$ is equal to\\
(1) $\sqrt { L _ { 1 } L _ { 2 } }$\\
(2) $\frac { L _ { 1 } + L _ { 2 } } { 2 }$\\
(3) $2 L _ { 1 } - L _ { 2 }$\\
(4) $3 L _ { 1 } - L _ { 2 }$