长方形面积与计算是小学几何知识的重要组成部分。我们知道：长方形面积＝长×宽，也就是说，通常情况下，要求长方形面积，应知道它的长和宽。但是，在不知长和宽的情况下，能不能求出长方形面积呢？南例一个长方形（如下图），被两条直线分成四个长方形，其中三个的面积分别 Rectangular area and calculation is an important part of primary school geometry. We know: rectangular area = length × width, that is, under normal circumstances, require rectangular area, should know its length and width. However, I do not know the length and width of the case, can not find a rectangular area? South Example A rectangle (pictured below) is divided into four rectangles by two straight lines, of which three are respectively