(2012•鹽城模擬)如圖a,在平面直角坐標(biāo)系中,A(0,6),B(4,0)
(1)按要求畫圖:在圖a中,以原點(diǎn)O為位似中心,按比例尺1:2,將△AOB縮小,得到△DOC,使△AOB與△DOC在原點(diǎn)O的兩側(cè);并寫出點(diǎn)A的對(duì)應(yīng)點(diǎn)D的坐標(biāo)為
(0,-3)
(0,-3)
,點(diǎn)B的對(duì)應(yīng)點(diǎn)C的坐標(biāo)為
(-2,0)
(-2,0)
;
(2)已知某拋物線經(jīng)過B、C、D三點(diǎn),求該拋物線的函數(shù)關(guān)系式,并畫出大致圖象;
(3)連接DB,若點(diǎn)P在CB上,從點(diǎn)C向點(diǎn)B以每秒1個(gè)單位運(yùn)動(dòng),點(diǎn)Q在BD上,從點(diǎn)B向點(diǎn)D以每秒1個(gè)單位運(yùn)動(dòng),若P、Q兩點(diǎn)同時(shí)分別從點(diǎn)C、點(diǎn)B點(diǎn)出發(fā),經(jīng)過t秒,當(dāng)t為何值時(shí),△BPQ是等腰三角形?