所有的圆都是相似图形.等圆能够相互重合,是全等形,当然相似;大小不同的两圆,将小圆放大一定倍数之后,可以和大圆变得相同而成为等圆,也相似.但不同的圆弧却未必相似,比如,一段优弧与一段劣弧相比,它们一定不相似,因为若两弧等长,则它们的曲率半径不同,即使一样长,也不会重合,一样长却不能重合的两段圆弧肯定不会相似的;若两弧不等长,将短弧放大一定倍数而与长弧长度相等之后,曲率半径仍不等,所以,它们也不相似. All the circles are similar, the circles can overlap each other, and they are congruent and of course similar. The two circles of different sizes can be similar to the circles if they are magnified by a certain multiple. However, different arcs may not be similar. For example, a segment of an arc may not be the same as a segment of a poor arc because, if two arcs are long, their radii of curvature are different and will not coincide even if they are as long as they are Long but can not overlap the two arcs will certainly not be similar; if the two arcs unequal length, the short arc enlarge a certain number of times and the length of the long arc equal, the radius of curvature is still not, so they are not similar.