江江松先生在他的新著《高中数学解题方法与技巧》一书的第十一章“不等式证明的常用方法”中例26用反证法证明了三角不等式：若a、β、γ为正锐角，且这是一种常规通法，下面提供一种巧妙的换元证法．注1本题的上界估计为：若a、＃、y为正锐角，且注2由上述证明容易得出改编的 Mr. Jiang Jiangsong proves the triangular inequality with the counter-evidence method in Chapter 11 “Methods and Techniques for Solving Inequalities of High School Mathematics” in his new book “Methods and Techniques of Solving Mathematical Problems in Senior High Schools”: if a, β, γ are positive Acute angle, and this is a common method, the following provides a clever way to change the evidence. Note 1 The upper bound of this problem is estimated as: if a, #, y are positive acute angles, and Note 2 is easily derived from the above proofs.