23.如圖1,在平面直角坐標(biāo)系中,拋物線y=
(x+3)(x-a)與x軸交于A,B(4,0)兩點(diǎn),點(diǎn)C在y軸上,且OC=OB,D,E分別是線段AC,AB上的動(dòng)點(diǎn)(點(diǎn)D,E不與點(diǎn)A,B,C重合).
(1)求此拋物線的表達(dá)式;
(2)連接DE并延長(zhǎng)交拋物線于點(diǎn)P,當(dāng)DE⊥x軸,且AE=1時(shí),求DP的長(zhǎng);
(3)連接BD.
①如圖2,將△BCD沿x軸翻折得到△BFG,當(dāng)點(diǎn)G在拋物線上時(shí),求點(diǎn)G的坐標(biāo);
②如圖3,連接CE,當(dāng)CD=AE時(shí),求BD+CE的最小值.