(2x＋y)^2-(x+2y)^2
=（2x＋y+x+2y)(2x＋y-x-2y）
=(3x+3y)(x-y)
=3(x+y)(x-y)
(2x+y)^2-(x+2y)^2
=(2x+y+x+2y)(2x+y-x-2y)
=(3x+3y)(x-y)
=3(x+y)(x-y)
：(2x+y)^2-(x+2y)^2
=[﹙2x＋y﹚＋﹙x＋2y﹚][﹙2x＋y﹚－﹙x＋2y﹚]
=﹙3x＋3y﹚﹙x－y﹚
=3﹙x＋y﹚﹙x－y﹚
(2x+y)^2-(x+2y)^2
=[(2x+y)-(x+2y)][(2x+y)+(x+2y)]
=(2x+y-x-2y)(2x+y+x+2y)
=(x-y)(3x+3y)
=3(x-y)(x+y)
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