1.(x+y)²-4（x+y-1)=(x+y)²-4(x+y)+4=(x+y)²-2×2(x+y)+2²=(x+y-2)²2.(x-y)²+4xy=x²-2xy+y²+4xy=x²+2xy+y²=(x+y)² 3.(x-1)(x+3)+1=x²+2x+1-3=(x+1)&su...