If $t _ { 1 }$ and $t _ { 2 }$ are the times of flight of two particles having the same initial velocity $u$ and range R on the horizontal, then $t _ { 1 } ^ { 2 } + t _ { 2 } ^ { 2 }$ is equal to\\
(1) $\frac { u ^ { 2 } } { g }$\\
(2) $\frac { 4 u ^ { 2 } } { g ^ { 2 } }$\\
(3) $\frac { u ^ { 2 } } { 2 g }$\\
(4) 1