例(2009年河北中考)如图1至图5,⊙O均作无滑动滚动,⊙O1,⊙O2,⊙O3,⊙O4均表示⊙O与线段AB或BC相切于端点时刻的位置,⊙O的周长为c.[阅读理解](1)如图1,⊙O从⊙O1的位置出发,沿AB滚动到⊙O2的位置,当AB=c时,⊙O恰好自转1周.(2)如图2,∠ABC相邻的补角是n°,⊙O在∠ABC外部沿A-B-C滚动,在点B处,必须由⊙O1的位置旋转到⊙O2的位置, Example (Hebei Senior High School Entrance Examination in 2009) As shown in Fig. 1 to Fig. 5, ⊙O are made with no sliding scroll, ⊙O1, ⊙O2, ⊙O3, ⊙O4 all indicate ⊙O and the line AB or BC tangential to the endpoint moment position, ⊙ O perimeter c. [Reading comprehension] (1) Figure 1, ⊙ O starting from the position of ⊙ O1, AB along the scroll to the ⊙ O2 position, when AB = c, ⊙ O exactly 1 rotation. (2) As shown in Fig. 2, 补ABC adjoining supplementary angle is n °, ⊙O scrolls along ABC outside ∠ABC, at point B, it must be rotated from ⊙O1 position to ⊙O2 position,