Cut a square diagonally into two identical triangles, the area of each triangle is 9 square centimeters, how long is the diagonal of this square in centimeters?
将一个正方形沿对角线剪成两个完全相同的三角形，每个三角形面积都是9平方厘米，原来这个正方形的对角线长多少厘米？
<result>6</result>