原式=﹛[﹙x+2y﹚﹙x-2y﹚]/﹙x+y﹚²﹜÷[﹙x+2y﹚/2x﹙x+y﹚]
=﹛[﹙x+2y﹚﹙x-2y﹚]/﹙x+y﹚²﹜×[2x﹙x+y﹚/﹙x+2y﹚]
=2x﹙x-2y﹚/﹙x+y﹚