25.已知,在平面直角坐標(biāo)系中,A(a,0),B(b,0)為x軸上兩點(diǎn),且a,b滿足:(a+6)
2+|a+b|=0,點(diǎn)
,∠ABC=30°,
,D為線段AB上一動(dòng)點(diǎn).
(1)求a,b的值;
(2)如圖1,若點(diǎn)D在BC的垂直平分線上,作∠ADE=120°,交AC的延長線于點(diǎn)E,連接BE,請判斷△BDE的形狀,并證明你的結(jié)論;
(3)如圖2,作點(diǎn)D關(guān)于BC的對稱點(diǎn)M,連接AM,取AM中點(diǎn)N,連接CN、CD,求CN的取值范圍.