24.如圖,在平面直角坐標(biāo)系中,已知點(diǎn)A坐標(biāo)為(6,0),點(diǎn)C坐標(biāo)為(2,4),以O(shè)A,OC為鄰邊作?ABCD,點(diǎn)P在對(duì)角線OB上,過(guò)點(diǎn)P作x軸的平行線分別交OC,AB于點(diǎn)D,E,過(guò)點(diǎn)P作PF⊥x軸于點(diǎn)F,設(shè)PF=a.
(1)求直線OC和直線OB的解析式;
(2)當(dāng)線段PD,PE,PF構(gòu)成的三角形是等腰三角形時(shí),求DP的值;
(3)取PE的中點(diǎn)Q,當(dāng)∠OQA=90°時(shí),求a的值.