(1)PQCD是平行四边形时,PD=CQ,即：AD-AP=CQ,24-T=3T,则T=6s
(2)PQCD是等腰梯形时,PQ=CD,即：CQ-PD=2(BC-AD),3T-(24-T)=2(26-24),即：则T=7s
(3)PQCD是直角梯形时,CQ-PD=BC-AD,3T-(24-T)=26-24,则T=6.5s