填空题 A 2 -B 2 =(A+B)(A-B)的充分必要条件是 1．
【正确答案】
【答案解析】AB=BA [解析] A 2 -B 2 =(A+B)(A-B)=A 2 +BA-AB-B 2 的充分必要条件是AB=BA．