23.如圖,在Rt△ABC中,∠ABC=90°,∠C=30°,AC=12cm,點(diǎn)E從點(diǎn)A出發(fā)沿AB以每秒1cm的速度向點(diǎn)B運(yùn)動(dòng),同時(shí)點(diǎn)D從點(diǎn)C出發(fā)沿CA以每秒2cm的速度向點(diǎn)A運(yùn)動(dòng),運(yùn)動(dòng)時(shí)間為t秒(0<t<6),過點(diǎn)D作DF⊥BC于點(diǎn)F.
(Ⅰ)試用含t的式子表示AE、AD、DF的長(zhǎng);
(Ⅱ)如圖①,連接EF,求證四邊形AEFD是平行四邊形;
(Ⅲ)如圖②,連接DE,當(dāng)t為何值時(shí),四邊形EBFD是矩形?并說明理由.