4﹙x＋y﹚²＋5－20﹙x＋y－1﹚
=4﹙x＋y﹚²＋5－20x-20y+20
=4﹙x＋y﹚²－20﹙x＋y)+25
=[2(x+y)-5]²
=(2x+2y-5)²