25(x+y)²+10(y+x)+1=[5(x+y)]²+2×5(x+y)×1+1²=[5(x+y)+1]²=(5x+5y+1)²
25(x-y)²+10(y-x)+1
=25(x-y)²-10(x-y)+1
=[5(x-y)]²-2×5(x-y)×1+1²
=[5(x-y)+1]²=(5x-5y+1)²