(1)∵D、E分别是AC、BD的中点,且AB=10,
∴DE=[1/2]AB=5;
(2)设A1B1=x,则A2B2=2x.
∵A1、A2是AC的三等分点,且A1B1∥A2B2∥AB,
∴A2B2是梯形A1ABB1的中位线,即:x+10=4x,得x=[10/3],
∴A1B1+A2B2=10;
(3)同理可得:A1B1+A2B2+…+A10B10=
10
11+
20
11+
30
11+…+
100
11=50.
(1)∵D、E分别是AC、BD的中点,且AB=10,
∴DE=[1/2]AB=5;
(2)设A1B1=x,则A2B2=2x.
∵A1、A2是AC的三等分点,且A1B1∥A2B2∥AB,
∴A2B2是梯形A1ABB1的中位线,即:x+10=4x,得x=[10/3],
∴A1B1+A2B2=10;
(3)同理可得:A1B1+A2B2+…+A10B10=
10
11+
20
11+
30
11+…+
100
11=50.