26.如圖,拋物線y=ax
2+bx+c經(jīng)過點(diǎn)A(-2,0),B(4,0),與y軸正半軸交于點(diǎn)C,且OC=2OA,拋物線的頂點(diǎn)為D,對稱軸交x軸于點(diǎn)E.直線y=mx+n經(jīng)過B,C兩點(diǎn).
(1)求拋物線及直線BC的函數(shù)表達(dá)式;
(2)點(diǎn)F是拋物線對稱軸上一點(diǎn),當(dāng)FA+FC的值最小時(shí),求出點(diǎn)F的坐標(biāo)及FA+FC的最小值;
(3)若點(diǎn)P是拋物線對稱軸上一點(diǎn),試探究是否存在以點(diǎn)P為直角頂點(diǎn)的Rt△APC,若存在,求出點(diǎn)P的坐標(biāo);若不存在,請說明理由.