\(tan^{-1}\left[\frac{cos~x}{1+sin~x} \right ]=\)
tan−1[cos x1+sin x]=tan−1[sin(π/2−x)1+cos(π/2−x)] =tan−1[2 sin(π/4)cos(π/4−x/2)2 cos2(π/4−x/2)] =tan−1tan(π4−x2)=π4−x2.