小题1:∠ACB = 45°,∠DEF = 90°,∴∠EQC = 45°. ∴EC =" EQ" = t,∴BE = 9-t .∴, (2分) 即: () 小题2:)①当DQ = DP时,∴6-t =10-3t,解得:t =" 2s." ········· (2分)
②当PQ = PD时,过P作,交DE于点H, 则DH = HQ=,由HP∥EF , ∴ 则,解得s·············· (2分) ③当QP = QD时,过Q作,交DP于点G, 则GD = GP=,可得:△DQG ∽△DFE , ∴,则,解得s 小题3:假设存在某一时刻t,使点P、Q、F三点在同一条直线上. 则,过P作,交BF于点I,∴PI∥DE, 于是:,∴,, ∴, 则,解得:s. 答:当s,点P、Q、F三点在同一条直线上. |