The function $f\left( x \right) = {\tan ^{ - 1}}\left( {\sin x + \cos x} \right)$ is an incresing function in
$\left( {0,{\pi \over 2}} \right)$
$\left( { - {\pi \over 2},{\pi \over 2}} \right)$
$\left( { {\pi \over 4},{\pi \over 2}} \right)$
$\left( { - {\pi \over 2},{\pi \over 4}} \right)$
