观察以下各式:
(x﹣y)(x+y)=x2﹣y2 .
(x﹣y)(x2+xy+y2)=x3﹣y3 .
(x﹣y)(x3+x2y+xy2+y3)=x4﹣y4 .
(x﹣y)(x4+x3y+x2y2+xy3+y4)=x5﹣y5 .
请回答以下问题: