The value of sin² 12° + sin² 21° + sin² 39° + sin² 48° - sin² 9° - sin² 18° is ______ .

${\sin }^2{12}^{\circ }+{\sin }^2{21}^{\circ }+{\sin }^2{39}^{\circ }+{\sin }^2{48}^{\circ }-{\sin }^2{9}^{\circ }-{\sin }^2{18}^{\circ }$
$={\sin }^2{12}^{\circ }+{\sin }^2{21}^{\circ }+\left({\sin }^2{39}^{\circ }-{\sin }^2{9}^{\circ }\right)+\left({\sin }^2{48}^{\circ }-{\sin }^2{18}^{\circ }\right)$
$=1-\left({\cos }^2{12}^{\circ }-{\sin }^2{21}^{\circ }\right)+\sin {48}^{\circ }\sin {30}^{\circ }+\sin {66}^{\circ }\sin {30}^{\circ }$