The deviation suffered by an oblique projectile is given by   $\delta =\frac{n{x}^2}{u^2{\cos }^2\theta }.$ The value of $n$  is ______
   
 

 $\tan \theta =\frac{AN}{ON}=\frac{y+\delta }{x}$
 $\Rightarrow \delta =x\tan \theta -y$
$\Rightarrow \delta =\left(x\tan \theta \right)-(x\tan \theta -\frac{g{x}^2}{2u^2{\cos }^2\theta })$
 $\Rightarrow \delta =\frac{1}{2}g{\left(\frac{x}{u\cos \theta }\right)}^2$
Since,  $x=\left(u\cos \theta \right)t$
 $\Rightarrow \delta =\frac{1}{2}g{t}^2$
Hence deviation suffered by an oblique projectile in time t (or in terms of x, u and launch angle  $\theta$) is
  $\delta =\frac{1}{2}g{t}^2=\frac{g{x}^2}{2u^2{\cos }^2\theta }$