“两边之和大于第三边”这是三角形三边关系的必然结果,可现在我们却发现了“两边之和等于第三边”的三角形。不妨先看题: 确定使a,a+1,a+2为钝角三角形的三边的a的取值范围。解要使a,a+1,a+2为三角形的三边,则必有a>0, “The sum of the two sides is greater than the third” This is the inevitable result of the trilateral relationship of the triangle, but now we have found the triangle “The sum of the two sides is equal to the third side.” Let’s look at the problem first: Determine the range of values ​​for a that make a, a+1, and a+2 be the three sides of an obtuse triangle. The solution is to make a, a+1, a+2 be the triangle’s three sides, then there must be a>0,