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九年义务教育教材《几何》第三册有一道“想一想”的问题：有一个半径为１０ｃｍ的大圆，另一个半径为２ｃｍ的小圆分别内切和外切滚动大圆一周，为什么内切小圆转动４周而外切小圆转动是６周．有文说，有些教师来信说想不通，叫大家作实验去．笔者拙想，有什么想不通呢？...
The book “Geometry” in the nine-year compulsory education textbook “Geometry” has a question of “thinking”: There is a large circle with a radius of 10cm, and another small circle with a radius of 2cm. The small circle rotates for 4 weeks and the outer circle rotates for 6 weeks. There are articles saying that some teachers have come up with a letter saying they can’t figure it out and tell everyone to experiment. The author thinks, what can’t be thought of? ...