12. 已知圆C:(x−3)2+(y−4)2=9C:(x-3)^{2}+(y-4)^{2}=9C:(x−3)2+(y−4)2=9和两点A(t,0)A(t,0)A(t,0),B(−tB(-tB(−t,0)(t>0)0)(t>0)0)(t>0),若圆CCC上至少存在一点PPP,使得PA→⋅PB→<0\overrightarrow{PA}\cdot \overrightarrow{PB}<0PA⋅PB<0,则实数ttt的取值范围是((( )))