边长为4cm的正方形ABCD绕它的顶点A旋转180°，顶点B所经过的路线长为____ cm．
- Could you tell me ________ he comes here?
- He drives here himself(他自己).
11×11= 21×31=
41×31= 51×51=
你发现什么规律了吗？用所发现的规律直接写出下面各题的得数．
21×21= 61×81= 91×31=
31×51= 41×41= 71×51=
