25.如圖所示,長(zhǎng)方形ABCD中,AB=4cm,AD=8cm.點(diǎn)P從點(diǎn)A出發(fā),沿邊AD向A-D-A做往返運(yùn)動(dòng),每秒移動(dòng)2cm,動(dòng)直線a與邊CD重合,交AD于點(diǎn)M,BC于點(diǎn)N.直線a與點(diǎn)P同時(shí)出發(fā),沿DA方向移動(dòng),每秒移動(dòng)1cm,移動(dòng)t秒(t>0),當(dāng)直線a與邊AB重合時(shí),移動(dòng)全部停止.
(1)用含t的代數(shù)式表示AP的長(zhǎng)度;
(2)當(dāng)t為何值時(shí),點(diǎn)P在直線a上;
(3)連結(jié)PB,PN,直接寫(xiě)出當(dāng)t為何值時(shí),△PAB與△PMN全等.