旋转是几何图形的三种图形变换之一,通过旋转,有利于把分散的几何条件集中在一起,然后运用旋转的“不变性”可以使一些难于下手的问题迎刃而解.一般来说,当图形中的某个三角形有一条边与某条线段具有公共的端点,且长度相等(简称共点等长)时,可以将该三角形绕着这个公共点旋转到等长的两边重合, Rotation is one of three graphics transformations of a geometry, which facilitates the convergence of decentralized geometry by rotation, and then resolves some difficult-to-start problems using the Rotational “invariance ” In general, When a triangle in an image has a common endpoint with a certain line segment and has the same length (ie, a total length of points, etc.), the triangle can be rotated around the common point to coincide with each other along the same length.