27.在平面中,對(duì)于點(diǎn)M,N,P,若∠MPN=90°,且PM=PN,則稱點(diǎn)P是點(diǎn)M和點(diǎn)N的“垂等點(diǎn)”.
在平面直角坐標(biāo)系xOy中,
(1)已知點(diǎn)M(-3,2),點(diǎn)N(1,0),則點(diǎn)P
1(0,3),P
2(-2,-1),P
3(-5,-2)中是點(diǎn)M和點(diǎn)N的“垂等點(diǎn)”的是
;
(2)已知點(diǎn)A(-4,0),B(0,b)(b>0).
①若在第二象限內(nèi)存在點(diǎn)C,使得點(diǎn)B是點(diǎn)A和點(diǎn)C的“垂等點(diǎn)”,寫出點(diǎn)C的坐標(biāo)(用含b的式子表示),并說(shuō)明理由;
②當(dāng)b=4時(shí),點(diǎn)D,點(diǎn)E是線段AO,BO上的動(dòng)點(diǎn)(點(diǎn)D,點(diǎn)E不與點(diǎn)A,B,O重合).若點(diǎn)F是點(diǎn)D和點(diǎn)E的“垂等點(diǎn)”,直接寫出點(diǎn)F的縱坐標(biāo)t的取值范圍.