如图，△A₁B₁C₁是边长为1的等边三角形，A₂为等边△A₁B₁C₁的中心，连接A₂B₁并延长到点B₂，使A₂B₁=B₁B₂，以A₂B₂为边作等边△A₂B₂C₂，A₃为等边

△A₂B₂C₂的中心，连接A₃B₂并延长到点B₃，使A₃B₂=B₂B₃，以A₃B₃为边作等边△A₃B₃C₃，依次作下去得到等边△A_nB_nC_n，则等边△A₅B₅C₅的边长为____．

补全对话

从方框中选择最佳选项完成对话, 有两项多余。

a. How are you?

b. What did you do in the camp?

c. Did you go there alone?

d. Can you play the violin now?

e. Where did you go on holiday?

f. Were there many students in the camp?

g. How long did you stay there?

M: Hey, Maria.____ 

W: I went to a music camp in Switzerland.

M: That sounds interesting.____ 

W: For ten days.

M: ____ 

W: We learned to play the piano, the guitar and the violin.

M:____ 

W: No. But I can play the guitar a little.

M:____ 

W: Yes, there were so many students. And they came from different cities.

“积善之家，大美余庆”．余庆人正在加快县城市化建设的步伐．某场馆建设工地上，工人用如图所示的滑轮组将重2000N的物体A以0.4m/s的速度沿水平方向匀速向前拉动2m，拉力F大小为250N，物体A与地面间的滑动摩擦力大小是物体A重力的0.2倍，求：