平面几何的证明问题中,有一类题目是关于线段的和差问题即证明两条线段的和(差)等于另一条线段.如果不能直接进行证明,则往往需要添加辅助线,而最常见的添加方法即为截长补短.截长补短就是在证题时,在长线段上截取和短线段相等的线段或把短线段补成和长线段相等的线段的引辅助线的方法.很多时候,同一题目的证明,既可截长,又可补短; One of the problems with proofs of plane geometry is about the sum-of-difference problems for line segments, which prove that the sum (difference) of the two line segments equals the other line segment. If you can not prove it directly, you often need to add a guideline, and the most common addition The method is to cut the length of the short cut short cut short is in the subject, the truncated in the long-term segment and the short-line segment equal to the short-line segment complement and long-line segment equal line guide line method .Many times , The same title of the proof, both cut length, but also make up short;