(x-2y)^2+16y-8x+16=(x-2y)^2-8x+16y+16=(x-2y)^2-8(x-2y)+16=[(x-2y)-4]^2=(x-2y-4)^2
(x-2y)²+16y-8x+16=(x-2y)²-8(x-2y)+16=(x-2y-4)² 如果不懂，请追问，祝学习愉快！
原式=(x-2y)²-8(x-2y)+16=(x-2y-4)²
