A trigonometric function !!!

Find the range of the following function :-

$f(\theta )\quad =\quad \sqrt { 8{ sin }^{ 2 }\theta +4cos^{ 2 }\theta -8{ sin }\theta cos\theta }$

$\bullet The\quad answer\quad can\quad be\quad expressed\quad in\quad the\quad form\quad of\quad \left[ \sqrt { A-\sqrt { B } } ,\sqrt { C+\sqrt { D } } \right] \quad where\quad B-A=14$

$\bullet Find\quad A+B+C+D$

$\bullet The\quad values\quad of\quad any\quad of\quad them\quad may\quad be\quad same\quad as\quad other.$