已知,(x+y)²-2x-2y+1 = (x+y)²-2(x+y)+1 = (x+y-1)² = 0 ,
可得：x+y-1 = 0 ,即有：x+y = 1 ；
所以,2x²+4xy+2y² = 2(x+y)² = 2 .