题目

一块等边三角形木板，边长为1，现将木板沿水平线翻滚，如图所示，若翻滚了20次．则B点所经过的路径长度为________． 答案：【答案】【解析】B点翻滚一周所走过的路径长度为两段弧长，一段是以点C为圆心，BC为半径，圆心角为120°，第二段是以A为圆心，AB为半径，圆心角为120°的两段弧长，依弧长公式计算即可．从图中发现：B点从开始至结束所走过的路径长度为两段弧长即第一段=，第二段=．故B点翻滚一周所走过的路径长Why have you asked us to do it again? As far as I can remember, we _______do that. A. are not able to　　　 B. weren't supposed to C. are likely to　　　 D. weren't able to