等弧，即相等的弧，九年义务教育初中几何第三册课本（下同）给出的定义是：在同圆或等圆中，能够互相重合的弧叫做等弧，记作。由定义可知：等弧存在于同圆或等圆中，在半径不等的圆中，不存在等弧。等弧是能够互相重合的弧，所以，等弧概念包含了三方面内容：l、必须在同圆或 Equal arcs, ie equal arcs, are defined in the 9th year compulsory education junior high school geometry Book 3 (the same below): In a circle or equal circle, arcs that can coincide with each other are called equal arcs. It can be known from the definition that equal arcs exist in the same circle or in a circle, and there is no equal arc in circles of unequal radius. Equal arcs are arcs that can coincide with each other, so the concept of equal arcs consists of three things: l, must be in the same circle or