As shown in the figure, P is the point on the fixed length line AB, and C and D respectively start from P and B and move to the left along the line AB at the speed of 1cm and 2cm per second. C is on the line AP D is on line BP (1) What is the quantitative relationship between the length of BD and PC? Explain the reason (2) If C and d move to any time, there will always be PD = 2Ac, please explain the position of point P on line AB! Figure: a -------- C --- P -------- D -------- B 20: 30, plus points!

PC=1t；BD=2t
∴BD=2PC
PD=PB-BD,AC=AP-PC
PD=2AC
∴PB-BD=2（AP-PC)=2AP-2PC
Also: BD = 2pc
∴PB=2AP
That is: P is one third of AB (AP = AB / 3)

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