“如果一个三角形的三条边长分别为a、b、c,且有a2+b2=c2,那么这个三角形是直角三角形.”这就是勾股定理的逆定理.它是初中几何中极其重要的一个定理,有着广泛的应用.下面举例说明.一、用于判断三角形的形状例1如图1,△ABC中,BC=a=2n+1,AC=b=2n2+2n,AB=c=2n2+2n+1.求证:△ABC是 “If a triangle has three sides a, b, and c, and a2+b2=c2, then this triangle is a right triangle.” This is the inverse theorem of the Pythagorean theorem. It is an extremely important one in junior geometry. Theorem has a wide range of applications. Here is an example. First, to determine the shape of a triangle Example 1 In Figure 1, △ABC, BC=a=2n+1, AC=b=2n2+2n, AB=c=2n2 +2n+1. Proof: △ABC is