(2)
若該拋物線上任意不同兩點(diǎn)M(x
1 , y
1),N(x
2 , y
2)都滿足:當(dāng)x
1<x
2<0時(shí),(x
1﹣x
2)(y
1﹣y
2)>0;當(dāng)0<x
1<x
2時(shí),(x
1﹣x
2)(y
1﹣y
2)<0.以原點(diǎn)O為心,OA為半徑的圓與拋物線的另兩個(gè)交點(diǎn)為B,C,且△ABC有一個(gè)內(nèi)角為60°.
①求拋物線的解析式;
②若點(diǎn)P與點(diǎn)O關(guān)于點(diǎn)A對(duì)稱(chēng),且O,M,N三點(diǎn)共線,求證:PA平分∠MPN.